Background of the Invention Ring laser gyroscopes are specialized interferometers that may be used to measure rotation.

These gyroscopes are applications of the Sagnac-type interferometer, and operate by propagating two beams of coherent light (e. g., which may be formed using a beam splitter) in opposite directions along the same optical path. Rotation of the interferometer creates a phase shift between the beams that is proportional to the angular velocity of the interferometer. When the two beams reach the same point along the optical path they interfere to create an interference pattern at an optical detector. This interference pattern shifts if the interferometer is rotated, thus making possible a rotation measurement.

In previously known laser gyroscopic systems, however, the components that make up the laser gyroscope (e. g., the laser, beam splitter, optical guide, detector, and any data processing

instrumentation) are manufactured separately and then electrically and optically coupled together, as necessary. Optical connections, such as between the laser and beam splitter, or between the beam splitter and the optical detector, require extreme precision, and are thus time consuming, and expensive, to manufacture. Also, electrical connections between components, such as the output of a detector and the input of a data processing instrument, are generally large and susceptible to failure when exposed to significant mechanical stress.

Accordingly, a need exists for a robust ring laser gyroscopic system that is lightweight, compact, inexpensive to manufacture, and capable of precision gyroscopic measurements.

Brief Description of the Drawings The present invention is illustrated by way of example and not limitation in the accompanying figures, in which like references indicate similar elements, and in which: FIGs. 1, 2,3,9,10 illustrate schematically, in cross section, device structures that can be used in accordance with various embodiments of the invention.

FIG. 4 illustrates graphically the relationship between maximum attainable film thickness and lattice mismatch between a host crystal and a grown crystalline overlayer.

FIG. 5 is a high resolution Transmission Electron Micrograph (TEM) of illustrative semiconductor

material manufactured in accordance with what is shown herein.

FIG. 6 is an x-ray diffraction taken on an illustrative semiconductor structure manufactured in accordance with what is shown herein.

FIG. 7 illustrates a high resolution Transmission Electron Micrograph of a structure including an amorphous oxide layer.

FIG. 8 illustrates an x-ray diffraction spectrum of a structure including an amorphous oxide layer.

FIGs. 11-15 include illustrations of cross- sectional views of a portion of an integrated circuit that includes a compound semiconductor portion, a bipolar portion, and an MOS portion in accordance with what is shown herein.

FIGs. 16-22 include illustrations of cross- sectional views of a portion of another integrated circuit that includes a semiconductor laser and a MOS transistor in accordance with what is shown herein.

FIG. 23 shows an illustrative example of a ring laser gyroscope that can be manufactured in accordance with the present invention.

FIG. 24 shows an enlarged view of an illustrative beam splitter region that can be used in a ring laser gyroscope in accordance with the present invention.

FIG. 25 shows another illustrative example of a ring laser gyroscope that can be manufactured in accordance with the present invention.

FIG. 26 shows yet another illustrative example of a ring laser gyroscope that can be manufactured in accordance with the present invention.

Skilled artisans will appreciate that in many cases elements in certain FIGs. are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in certain FIGs. may be exaggerated relative to other elements to help to improve understanding of what is being shown Detailed Description of the Invention This invention relates to a ring laser gyroscopic structures, devices, and circuits that can be substantially constructed on a single piece of monolithic semiconductor material.

As discussed more fully below, a ring laser gyroscope structure according to this invention at least includes a semiconductor substrate, a beam splitter region, a waveguide, and a detector. An integrated laser can also be integrated on the substrate. The beam splitter region is on the substrate and includes a beam splitting element, an input for receiving a laser beam, a first optical port, a second optical port, and a detector port. The waveguide, which is also on the substrate, couples the first and second optical ports. The optical detector, also on said substrate, has an input that is optically coupled to the waveguide detector port. An integrated circuit for processing data generated by the optical detector can also be included. By detecting the

interference pattern with an array of photosensitive elements, the data can be fit to a mathematical model of the interference pattern. The fit is then used to determine the system rotational parameter, such as the angle of rotation or angular velocity.

Before discussing the ring laser gyroscope circuit in more detail, a discussion of various semiconductor and other structures, as well as the material processing techniques used to form them, is provided.

The present invention involves semiconductor structures of particular types. For convenience herein, these semiconductor structures are sometimes referred to as"composite semiconductor structures"or "composite integrated circuits"because they include two (or more) significantly different types of semiconductor devices in one integrated structure or circuit. For example, one of these two types of devices may be silicon-based devices such as CMOS devices, and the other'of these two types of devices may be compound semiconductor devices such GaAs devices. Illustrative composite semiconductor structures and methods for making such structures are disclosed in Ramdani et al. U. S. patent application No.

09/502,023, filed February 10,2000, which is hereby incorporated by reference herein in its entirety.

Certain material from that reference is substantially repeated below to ensure that there is support herein for references to composite semiconductor structures and composite integrated circuits.

FIG. 1 illustrates schematically, in cross section, a portion of a semiconductor structure 20 which may be relevant to or useful in connection with certain embodiments of the present invention.

Semiconductor structure 20 includes a monocrystalline substrate 22, accommodating buffer layer 24 comprising a monocrystalline material, and a layer 26 of a monocrystalline compound semiconductor material. In this context, the term"monocrystalline"shall have the meaning commonly used within the semiconductor industry. The term shall refer to materials that are a single crystal or that are substantially a single crystal and shall include those materials having a relatively small number of defects such as dislocations and the like as are commonly found in substrates of silicon or germanium or mixtures of silicon and germanium and epitaxial layers of such materials commonly found in the semiconductor industry.

In accordance with one embodiment, structure 20 also includes an amorphous intermediate layer 28 positioned between substrate 22 and accommodating buffer layer 24. Structure 20 may also include a template layer 30 between accommodating buffer layer 24 and compound semiconductor layer 26. As will be explained more fully below, template layer 30 helps to initiate the growth of compound semiconductor layer 26 on accommodating buffer layer 24. Amorphous intermediate layer 28 helps to relieve the strain in accommodating buffer layer 24 and by doing so, aids in the growth of a high crystalline quality accommodating buffer layer 24.

Substrate 22, in accordance with one embodiment, is a monocrystalline semiconductor wafer, preferably of large diameter. The wafer can be of a material from Group IV of the periodic table, and preferably a material from Group IVA. Examples of Group IV semiconductor materials include silicon, germanium, mixed silicon and germanium, mixed silicon and carbon, mixed silicon, germanium and carbon, and the like. Preferably substrate 22 is a wafer containing silicon or germanium, and most preferably is a high quality monocrystalline silicon wafer as used in the semiconductor industry. Accommodating buffer layer 24 is preferably a monocrystalline oxide or nitride material epitaxially grown on the underlying substrate 22. In accordance with one embodiment, amorphous intermediate layer 28 is grown on substrate 22 at the interface between'substrate 22 and the growing accommodating buffer layer 24 by the oxidation of substrate 22 during the growth of layer 24.

Amorphous intermediate layer 28 serves to relieve strain that might otherwise occur in monocrystalline accommodating buffer layer 24 as a result of differences in the lattice constants of substrate 22 and buffer layer 24. As used herein, lattice constant refers to the distance between atoms of a cell measured in the plane of the surface. If such strain is not relieved by amorphous intermediate layer 28, the strain may cause defects in the crystalline structure of accommodating buffer layer 24. Defects in the crystalline structure of accommodating buffer layer 24, in turn, would make it difficult to achieve a high

quality crystalline structure in monocrystalline compound semiconductor layer 26.

Accommodating buffer layer 24 is preferably a monocrystalline oxide or nitride material selected for its crystalline compatibility with underlying substrate 22 and with overlying compound semiconductor material 26. For example, the material could be an oxide or nitride having a lattice structure matched to substrate 22 and to the subsequently applied semiconductor material 26. Materials that are suitable for accommodating buffer layer 24 include metal oxides such as the alkaline earth metal titanates, alkaline earth metal zirconates, alkaline earth metal hafnates, alkaline earth metal tantalates, alkaline earth metal ruthenates, alkaline earth metal niobates, alkaline earth metal vanadates, perovskite oxides such as alkaline earth metal tin-based perovskites, lanthanum aluminate, lanthanum scandium oxide, and gadolinium oxide. Additionally, various nitrides such as gallium nitride, aluminum nitride, and boron nitride may also be used for accommodating buffer layer 24. Most of these materials are insulators, although strontium ruthenate, for example, is a conductor. Generally, these materials are metal oxides or metal nitrides, and more particularly, these metal oxide or nitrides typically include at least two different metallic elements. In some specific applications, the metal oxides or nitride may include three or more different metallic elements.

Amorphous interface layer 28 is preferably an oxide formed by the oxidation of the surface of

substrate 22, and more preferably is composed of a silicon oxide. The thickness of layer 28 is sufficient to relieve strain attributed to mismatches between the lattice constants of substrate 22 and accommodating buffer layer 24. Typically, layer 28 has a thickness in the range of approximately 0.5-5 nm.

The compound semiconductor material of layer 26 can be selected, as needed for a particular semiconductor structure, from any of the Group IIIA and VA elements (III-V semiconductor compounds), mixed III- V compounds, Group II (A or B) and VIA elements (II-VI semiconductor compounds), and mixed II-VI compounds.

Examples include gallium arsenide (GaAs), gallium indium arsenide (GaInAs), gallium aluminum arsenide (GaAlAs), indium phosphide (InP), cadmium sulfide (CDs), cadmium mercury telluride (CdHgTe), zinc selenide (ZnSe), zinc sulfur selenide (ZnSSe), and the like. Suitable template 30 materials chemically bond to the surface of the accommodating buffer layer 24 at selected sites and provide sites for the nucleation of the epitaxial growth of the subsequent compound semiconductor layer 26. Appropriate materials for template 30 are discussed below.

FIG. 2 illustrates, in cross section, a portion of a semiconductor structure 40 in accordance with a further embodiment. Structure 40 is similar to the previously described semiconductor structure 20 except that an additional buffer layer 32 is positioned between accommodating buffer layer 24 and layer of monocrystalline compound semiconductor material 26.

Specifically, additional buffer layer 32 is positioned

between the template layer 30 and the overlying layer 26 of compound semiconductor material.

Additional buffer layer 32, formed of a semiconductor or compound semiconductor material, serves to provide a lattice compensation when the lattice constant of accommodating buffer layer 24 cannot be adequately matched to the overlying monocrystalline compound semiconductor material layer 26.

FIG. 3 schematically illustrates, in cross section, a portion of a semiconductor structure 34 in accordance with another exemplary embodiment of the invention. Structure 34 is similar to structure 20, except that structure 34 includes an amorphous layer 36, rather than accommodating buffer layer 24 and amorphous interface layer 28, and an additional semiconductor layer 38.

As explained in greater detail below, amorphous layer 36 may be formed by first forming an accommodating buffer layer and an amorphous interface layer in a similar manner to that described above.

Monocrystalline semiconductor layer 26 is then formed (by epitaxial growth) overlying the monocrystalline accommodating buffer layer. The accommodating buffer layer is then exposed to an anneal process to convert the monocrystalline accommodating buffer layer to an amorphous layer. Amorphous layer 36 formed in this manner comprises materials from both the accommodating buffer and interface layers, which amorphous layers may or may not amalgamate. Thus, layer 36 may comprise one or two amorphous layers. Formation of amorphous layer 36 between substrate 22 and semiconductor layer 38

(subsequent to layer 38 formation) relieves stresses between layers 22 and 38 and provides a true compliant substrate for subsequent processing--e. g., compound semiconductor layer 26 formation.

The processes previously described above in connection with FIGS. 1 and 2 are adequate for growing monocrystalline compound semiconductor layers over a monocrystalline substrate. However, the process described in connection with FIG. 3, which includes transforming a monocrystalline accommodating buffer layer to an amorphous oxide layer, may be better for growing monocrystalline compound semiconductor layers because it allows any strain in layer 26 to relax.

Semiconductor layer 38 may include any of the materials described throughout this application in connection with either of compound semiconductor material layer 26 or additional buffer layer 32. For example, layer 38 may include monocrystalline Group IV or monocrystalline compound semiconductor materials.

In accordance with one embodiment of the present invention, semiconductor layer 38 serves as an anneal cap during layer 36 formation and as a template for subsequent semiconductor layer 26 formation.

Accordingly, layer 38 is preferably thick enough to provide a suitable template for layer 26 growth (at least one monolayer) and thin enough to allow layer 38 to form as a substantially defect free monocrystalline semiconductor compound.

In accordance with another embodiment of the invention, semiconductor layer 38 comprises compound semiconductor material (e. g., a material discussed

above in connection with compound semiconductor layer 26) that is thick enough to form devices within layer 38. In this case, a semiconductor structure in accordance with the present invention does not include compound semiconductor layer 26. In other words, the semiconductor structure in accordance with this embodiment only includes one compound semiconductor layer disposed above amorphous oxide layer 36.

The layer formed on substrate 22, whether it includes only accommodating buffer layer 24, accommodating buffer layer 24 with amorphous intermediate or interface layer 28, or an amorphous layer such as layer 36 formed by annealing layers 24 and 28 as described above in connection with FIG. 3, may be referred to generically as an"accommodating layer." The following non-limiting, illustrative examples illustrate various combinations of materials useful in structures 20,40 and 34 in accordance with various alternative embodiments. These examples are merely illustrative, and it is not intended that the invention be limited to these illustrative examples.

Example 1 In accordance with one embodiment, monocrystalline substrate 22 is a silicon substrate oriented in the (100) direction. Silicon substrate 22 can be, for example, a silicon substrate as is commonly used in making complementary metal oxide semiconductor (CMOS) integrated circuits having a diameter of

about 200-300 mm. In accordance with this embodiment, accommodating buffer layer 24 is a monocrystalline layer of SrzBalzTiO3 where z ranges from 0 to 1 and amorphous intermediate layer 28 is a layer of silicon oxide (SiOx) formed at the interface between silicon substrate 22 and accommodating buffer layer 24. The value of z is selected to obtain one or more lattice constants closely matched to corresponding lattice constants of the subsequently formed layer 26.

Accommodating buffer layer 24 can have a thickness of about 2 to about 100 nanometers (nm) and preferably has a thickness of about 10 nm. In general, it is desired to have an accommodating buffer layer 24 thick enough to isolate compound semiconductor layer 26 from substrate 22 to obtain the desired electrical and optical properties. Layers thicker than 100 nm usually provide little additional benefit while increasing cost unnecessarily; however, thicker layers may be fabricated if needed. The amorphous intermediate layer 28 of silicon oxide can have a thickness of about 0.5-5 nm, and preferably a thickness of about 1.5-2.5 nm.

In accordance with this embodiment, compound semiconductor material layer 26 is a layer of gallium arsenide (GaAs) or aluminum gallium arsenide (AlGaAs) having a thickness of about 1 nm to about 100 micrometers (pm) and preferably a thickness of about 0.5 pm to 10 pm. The thickness generally depends on the application for which the layer is being prepared.

To facilitate the epitaxial growth of the gallium arsenide or aluminum gallium arsenide on the

monocrystalline oxide, a template layer 30 is formed by capping the oxide layer. Template layer 30 is preferably 1-10 monolayers of Ti-As, Sr-O-As, Sr-Ga-0, or Sr-Al-O. By way of a preferred example, 1-2 monolayers 30 of Ti-As or Sr-Ga-0 have been shown to successfully grow GaAs layers 26.

Example 2 In accordance with a further embodiment, monocrystalline substrate 22 is a silicon substrate as described above. Accommodating buffer layer 24 is a monocrystalline oxide of strontium or barium zirconate or hafnate in a cubic or orthorhombic phase with an amorphous intermediate layer 28 of silicon oxide formed at the interface between silicon substrate 22 and accommodating buffer layer 24. Accommodating buffer layer 24 can have a thickness of about 2-100 nm and preferably has a thickness of at least 5 nm to ensure adequate crystalline and surface quality and is formed of a monocrystalline SrZr03, BaZrO3, SrHfO3, BaSnO3 or BaHf03. For example, a monocrystalline oxide layer of BaZrO3 can grow at a temperature of about 700 degrees C. The lattice structure of the resulting crystalline oxide exhibits a 45 degree rotation with respect to the substrate 22 silicon lattice structure.

An accommodating buffer layer 24 formed of these zirconate or hafnate materials is suitable for the growth of compound semiconductor materials 26 in the indium phosphide (InP) system. The compound semiconductor material 26 can be, for example, indium

phosphide (InP), indium gallium arsenide (InGaAs), aluminum indium arsenide, (AlInAs), or aluminum gallium indium arsenic phosphide (AlGaInAsP), having a thickness of about 1. 0 nm to 10 Zm. A suitable template 30 for this structure is 1-10 monolayers of zirconium-arsenic (Zr-As), zirconium-phosphorus (Zr-P), hafnium-arsenic (Hf-As), hafnium-phosphorus (Hf-P), strontium-oxygen-arsenic (Sr-O-As), strontium-oxygen- phosphorus (Sr-O-P), barium-oxygen-arsenic (Ba-O-As), indium-strontium-oxygen (In-Sr-O), or barium-oxygen- phosphorus (Ba-O-P), and preferably 1-2 monolayers of one of these materials. By way of an example, for a barium zirconate accommodating buffer layer 24, the surface is terminated with 1-2 monolayers of zirconium followed by deposition of 1-2 monolayers of arsenic to form a Zr-As template 30. A monocrystalline layer 26 of the compound semiconductor material from the indium phosphide system is then grown on template layer 30.

The resulting lattice structure of the compound semiconductor material 26 exhibits a 45 degree rotation with respect to the accommodating buffer layer 24 lattice structure and a lattice mismatch to (100) InP of less than 2.5%, and preferably less than about 1. 0%.

Example 3 In accordance with a further embodiment, a structure is provided that is suitable for the growth of an epitaxial film of a II-VI material overlying a silicon substrate 22. The substrate 22 is preferably a silicon wafer as described above. A suitable

accommodating buffer layer 24 material is SrxBal-xTi03, where x ranges from 0 to 1, having a thickness of about 2-100 nm and preferably a thickness of about 5-15 nm.

The II-VI compound semiconductor material 26 can be, for example, zinc selenide (ZnSe) or zinc sulfur selenide (ZnSSe). A suitable template 30 for this material system includes 1-10 monolayers of zinc-oxygen (Zn-0) followed by 1-2 monolayers of an excess of zinc followed by the selenidation of zinc on the surface.

Alternatively, a template 30 can be, for example, 1-10 monolayers of strontium-sulfur (Sr-S) followed by the ZnSeS.

Example 4 This embodiment of the invention is an example of structure 40 illustrated in FIG. 2.

Substrate 22, monocrystalline oxide layer 24, and monocrystalline compound semiconductor material layer 26 can be similar to those described in example 1. In addition, an additional buffer layer 32 serves to alleviate any strains that might result from a mismatch of the crystal lattice of the accommodating buffer layer and the lattice of the monocrystalline semiconductor material. Buffer layer 32 can be a layer of germanium or a GaAs, an aluminum gallium arsenide (AlGaAs), an indium gallium phosphide (InGaP), an aluminum gallium phosphide (AlGaP), an indium gallium arsenide (InGaAs), an aluminum indium phosphide (AlInP), a gallium arsenide phosphide (GaAsP), or an indium gallium phosphide (InGaP) strain compensated

superlattice. In accordance with one aspect of this embodiment, buffer layer 32 includes a GaAsxPl-x superlattice, wherein the value of x ranges from 0 to 1. In accordance with another aspect, buffer layer 32 includes an InyGal_yP superlattice, wherein the value of y ranges from 0 to 1. By varying the value of x or y, as the case may be, the lattice constant is varied from bottom to top across the superlattice to create a match between lattice constants of the underlying oxide and the overlying compound semiconductor material. The compositions of other materials, such as those listed above, may also be similarly varied to manipulate the lattice constant of layer 32 in a like manner. The superlattice can have a thickness of about 50-500 nm and preferably has a thickness of about 100-200 nm. The template for this structure can be the'same of that'described in example 1. Alternatively, buffer layer 32 can be a layer of monocrystalline germanium having a thickness of 1-50 nm and preferably having a thickness of about 2-20 nm. In using a germanium buffer layer, a template layer of either germanium-strontium (Ge-Sr) or germanium- titanium (Ge-Ti) having a thickness of about one monolayer can be used as a nucleating site for the subsequent growth of the monocrystalline compound semiconductor material layer. The formation of the oxide layer is capped with either a monolayer of strontium or a monolayer of titanium to act as a nucleating site for the subsequent deposition of the monocrystalline germanium. The monolayer of strontium

or titanium provides a nucleating site to which the first monolayer of germanium can bond.

Example 5 This example also illustrates materials useful in a structure 40 as illustrated in FIG. 2.

Substrate material 22, accommodating buffer layer 24, monocrystalline compound semiconductor material layer 26 and template layer 30 can be the same as those described above in example 2. In addition, a buffer layer 32 is inserted between accommodating buffer layer 24 and overlying monocrystalline compound semiconductor material layer 26. Buffer layer 32, a further monocrystalline semiconductor material, can be, for example, a graded layer of indium gallium arsenide (InGaAs) or indium aluminum arsenide (InAlAs). In accordance with one aspect of this embodiment, buffer layer 32 includes InGaAs, in which the indium composition varies from 0 to about 47%. Buffer layer 32 preferably has a thickness of about 10-30 nm.

Varying the composition of buffer layer 32 from GaAs to InGaAs serves to provide a lattice match between the underlying monocrystalline oxide material 24 and the overlying layer 26 of monocrystalline compound semiconductor material. Such a buffer layer 32 is especially advantageous if there is a lattice mismatch between accommodating buffer layer 24 and monocrystalline compound semiconductor material layer 26.

Example 6

This example provides exemplary materials useful in structure 34, as illustrated in FIG. 3.

Substrate material 22, template layer 30, and monocrystalling compound semiconductor material layer 26 may be the same as those described above in connection with example 1.

Amorphous layer 36 is an amorphous oxide layer which is suitably formed of a combination of amorphous intermediate layer materials (e. g., layer 28 materials as described above) and accommodating buffer layer materials (e. g., layer 24 materials as described above). For example, amorphous layer 36 may include a combination of SiOx and SrzBal-z Ti03 (where z ranges from 0 to 1), which combine or mix, at least partially, during an anneal process to form amorphous oxide layer 36.

The thickness of amorphous layer 36 may vary from application to application and may depend on such factors as desired insulating properties of layer 36, type of semiconductor material comprising layer 26, and the like. In accordance with one exemplary aspect of the present embodiment, layer 36 thickness is about 2 nm to about 100 nm, preferably about 2-10 nm, and more preferably about 5-6 nm.

Layer 38 comprises a monocrystalline compound semiconductor material that can be grown epitaxially over a monocrystalline oxide material such as material used to form accommodating buffer layer 24. In accordance with one embodiment of the invention, layer 38 includes the same materials as those comprising

layer 26. For example, if layer 26 includes GaAs, layer 38 also includes GaAs. However, in accordance with other embodiments of the present invention, layer 38 may include materials different from those used to form layer 26. In accordance with one exemplary embodiment of the invention, layer 38 is about 1 monolayer to about 100 nm thick.

Referring again to FIGS. 1-3, substrate 22 is a monocrystalline substrate such as a monocrystalline silicon substrate. The crystalline structure of the monocrystalline substrate is characterized by a lattice constant and by a lattice orientation. In similar manner, accommodating buffer layer 24 is also a monocrystalline material and the lattice of that monocrystalline material is characterized by a lattice constant and a crystal orientation. The lattice constants of accommodating buffer layer 24 and monocrystalline substrate 22 must be closely matched or, alternatively, must be such that upon rotation of one crystal orientation with respect to the other crystal orientation, a substantial match in lattice constants is achieved. In this context the terms "substantially equal"and"substantially matched"mean that there is sufficient similarity between the lattice constants to permit the growth of a high quality crystalline layer on the underlying layer.

FIG. 4 illustrates graphically the relationship of the achievable thickness of a grown crystal layer of high crystalline quality as a function of the mismatch between the lattice constants of the host crystal and the grown crystal. Curve 42

illustrates the boundary of high crystalline quality material. The area to the right of curve 42 represents layers that tend to be polycrystalline. With no lattice mismatch, it is theoretically possible to grow an infinitely thick, high quality epitaxial layer on the host crystal. As the mismatch in lattice constants increases, the thickness of achievable, high quality crystalline'layer decreases rapidly. As a reference point, for example, if the lattice constants between the host crystal and the grown layer are mismatched by more than about 2%, monocrystalline epitaxial layers in excess of about 20 nm cannot be achieved.

In accordance with one embodiment, substrate 22 is a (100) or (111) oriented monocrystalline silicon wafer and accommodating buffer layer 24 is a layer of strontium barium titanate. Substantial matching of lattice constants between these two materials is achieved by rotating the crystal orientation of the titanate material 24 by 45'witch respect to the crystal orientation of the silicon substrate wafer 22. The inclusion in the structure of amorphous interface layer 28, a silicon oxide layer in this example, if it is of sufficient thickness, serves to reduce strain in the titanate monocrystalline layer 24 that might result from any mismatch in the lattice constants of the host silicon wafer 22 and the grown titanate layer 24. As a result, a high quality, thick, monocrystalline titanate layer 24 is achievable.

Still referring to FIGS. 1-3, layer 26 is a layer of epitaxially grown monocrystalline material and that crystalline material is also characterized by a

crystal lattice constant and a crystal orientation. In accordance with one embodiment of the invention, the lattice constant of layer 26 differs from the lattice constant of substrate 22. To achieve high crystalline quality in this epitaxially grown monocrystalline layer, accommodating buffer layer 24 must be of high crystalline quality. In addition, in order to achieve high crystalline quality in layer 26, substantial matching between the crystal lattice constant of the host crystal, in this case, monocrystalline accommodating buffer layer 24, and grown crystal 26 is desired. With properly selected materials this substantial matching of lattice constants is achieved as a result of rotation of the crystal orientation of grown crystal 26 with respect to the orientation of host crystal 24. If grown crystal 26 is gallium arsenide, aluminum gallium arsenide, zinc selenide, or zinc sulfur selenide and accommodating buffer layer 24 is monocrystalline SrxBal-xTi03, substantial matching of crystal lattice constants of the two materials is achieved, wherein the crystal orientation of grown layer 26 is rotated by 45° with respect to the orientation of the host monocrystalline oxide 24.

Similarly, if host material 24 is a strontium or barium zirconate or a strontium or barium hafnate or barium tin oxide and compound semiconductor layer 26 is indium phosphide or gallium indium arsenide or aluminum indium arsenide, substantial matching of crystal lattice constants can be achieved by rotating the orientation of grown crystal layer 26 by 45° with respect to host oxide crystal 24. In some instances,

a crystalline semiconductor buffer layer 32 between host oxide 24 and grown compound semiconductor layer 26 can be used to reduce strain in grown monocrystalline compound semiconductor layer 26 that might result from small differences in lattice constants. Better crystalline quality in grown monocrystalline compound semiconductor layer 26 can thereby be achieved.

The following example illustrates a process, in accordance with one embodiment, for fabricating a semiconductor structure such as the structures depicted in FIGS. 1-3. The process starts by providing a monocrystalline semiconductor substrate 22 comprising silicon or germanium. In accordance with a preferred embodiment, semiconductor substrate 22 is a silicon wafer having a (100) orientation. Substrate 22 is preferably oriented on axis or, at most, about 0.5° off axis. At least a portion of semiconductor substrate 22 has a bare surface, although other portions of the substrate, as described below, may encompass other structures. The term"bare"in this context means that the surface in the portion of substrate 22 has been cleaned to remove any oxides, contaminants, or other foreign material. As is well known, bare silicon is highly reactive and readily forms a native oxide. The term"bare"is intended to encompass such a native oxide. A thin silicon oxide may also be intentionally grown on the semiconductor substrate, although such a grown oxide is not essential to the process. In order to epitaxially grow a monocrystalline oxide layer 24 overlying monocrystalline substrate 22, the native oxide layer must first be removed to expose the

crystalline structure of underlying substrate 22. The following process is preferably carried out by molecular beam epitaxy (MBE), although other epitaxial processes may also be used in accordance with the present invention. The native oxide can be removed by first thermally depositing a thin layer of strontium, barium, a combination of strontium and barium, or other alkali earth metals or combinations of alkali earth metals in an MBE apparatus. In the case where strontium is used, the substrate 22 is then heated to a temperature of about 750°C to cause the strontium to react with the native silicon oxide layer. The strontium serves to reduce the silicon oxide to leave a silicon oxide-free surface. The resultant surface, which exhibits an ordered 2x1 structure, includes strontium, oxygen, and silicon. The ordered 2x1 structure forms a template for the ordered growth of an overlying layer 24 of a monocrystalline oxide. The template provides the necessary chemical and physical properties to nucleate the crystalline growth of an overlying layer 24.

In accordance with an alternate embodiment, the native silicon oxide can be converted and the surface of substrate 22 can be prepared for the growth of a monocrystalline oxide layer 24 by depositing an alkali earth metal oxide, such as strontium oxide or barium oxide, onto the substrate surface by MBE at a low temperature and by subsequently heating the structure to a temperature of about 750°C. At this temperature a solid state reaction takes place between the strontium oxide and the native silicon oxide

causing the reduction of the native silicon oxide and leaving an ordered 2x1 structure with strontium, oxygen, and silicon remaining on the substrate 22 surface. Again, this forms a template for the subsequent growth of an ordered monocrystalline oxide layer 24.

Following the removal of the silicon oxide from the surface of substrate 22, the substrate is cooled to a temperature in the range of about 200-800°C and a layer 24 of strontium titanate is grown on the template layer by molecular beam epitaxy. The MBE process is initiated by opening shutters in the MBE apparatus to expose strontium, titanium and oxygen sources. The ratio of strontium and titanium is approximately 1: 1. The partial pressure of oxygen is initially set at a minimum value to grow stochiometric strontium titanate at a growth rate of about 0.3-0.5 nm per minute. After initiating growth of the strontium titanate, the partial pressure of oxygen is increased above the initial minimum value. The overpressure of oxygen causes the growth of an amorphous silicon oxide layer 28 at the interface between underlying substrate 22 and the growing strontium titanate layer 24. The growth of silicon oxide layer 28 results from the diffusion of oxygen through the growing strontium titanate layer 24 to the interface where the oxygen reacts with silicon at the surface of underlying substrate 22. The strontium titanate grows as an ordered monocrystal 24 with the crystalline orientation rotated by 45° with respect to the ordered 2x1 crystalline structure of underlying substrate 22.

Strain that otherwise might exist in strontium titanate layer 24 because of the small mismatch in lattice constant between silicon substrate 22 and the growing crystal 24 is relieved in amorphous silicon oxide intermediate layer 28.

After strontium titanate layer 24 has been grown to the desired thickness, the monocrystalline strontium titanate is capped by a template layer 30 that is conducive to the subsequent growth of an epitaxial layer of a desired compound semiconductor material 26. For the subsequent growth of a layer 26 of gallium arsenide, the MBE growth of strontium titanate monocrystalline layer 24 can be capped by terminating the growth with 1-2 monolayers of titanium, 1-2 monolayers of titanium-oxygen or with 1-2 monolayers of strontium-oxygen. Following the formation of this capping layer, arsenic is deposited to form a Ti-As bond, a Ti-O-As bond or a Sr-O-As. Any of these form an appropriate template 30 for deposition and formation of a gallium arsenide monocrystalline layer 26. Following the formation of template 30, gallium is subsequently introduced to the reaction with the arsenic and gallium arsenide 26 forms.

Alternatively, gallium can be deposited on the capping layer to form a Sr-O-Ga bond, and arsenic is subsequently introduced with the gallium to form the GaAs.

FIG. 5 is a high resolution Transmission Electron Micrograph (TEM) of semiconductor material manufactured in accordance with the present invention.

Single crystal SrTi03 accommodating buffer layer 24

was grown epitaxially on silicon substrate 22. During this growth process, amorphous interfacial layer 28 is formed which relieves strain due to lattice mismatch.

GaAs compound semiconductor layer 26 was then grown epitaxially using template layer 30.

FIG. 6 illustrates an x-ray diffraction spectrum taken on structure including GaAs compound semiconductor layer 26 grown on silicon substrate 22 using accommodating buffer layer 24. The peaks in the spectrum indicate that both the accommodating buffer layer 24 and GaAs compound semiconductor layer 26 are single crystal and (100) orientated.

The structure illustrated in FIG. 2 can be formed by the process discussed above with the addition of an additional buffer layer 32 deposition step.

Buffer layer 32 is formed overlying template layer 30 before the deposition of monocrystalline compound semiconductor layer 26. If buffer layer 32 is a compound semiconductor superlattice, such a superlattice can be deposited, by MBE for example, on the template 30 described above. If instead buffer layer 32 is a layer of germanium, the process above is modified to cap strontium titanate monocrystalline layer 24 with a final layer of either strontium or titanium and then by depositing germanium to react with the strontium or titanium. The germanium buffer layer 32 can then be deposited directly on this template 30.

Structure 34, illustrated in FIG. 3, may be formed by growing an accommodating buffer layer, forming an amorphous oxide layer over substrate 22, and

growing semiconductor layer 38 over the accommodating buffer layer, as described above. The accommodating buffer layer and the amorphous oxide layer are then exposed to an anneal process sufficient to change the crystalline structure of the accommodating buffer layer from monocrystalline to amorphous, thereby forming an amorphous layer such that the combination of the amorphous oxide layer and the now amorphous accommodating buffer layer form a single amorphous oxide layer 36. Layer 26 is then subsequently grown over layer 38. Alternatively, the anneal process may be carried out subsequent to growth of layer 26.

In accordance with one aspect of this embodiment, layer 36 is formed by exposing substrate 22, the accommodating buffer layer, the amorphous oxide layer, and semiconductor layer 38 to a rapid thermal anneal process with a peak temperature of about 700°C to about 1000°C and a process time of about 1 to about 10 minutes. However, other suitable anneal processes may be employed to convert the accommodating buffer layer to an amorphous layer in accordance with the present invention. For example, laser annealing or "conventional"thermal annealing processes (in the proper environment) may be used to form layer 36. When conventional thermal annealing is employed to form layer 36, an overpressure of one or more constituents of layer 30 may be required to prevent degradation of layer 38 during the anneal process. For example, when layer 38 includes GaAs, the anneal environment preferably includes an overpressure of arsenic to mitigate degradation of layer 38.

As noted above, layer 38 of structure 34 may include any materials suitable for either of layers 32 or 26. Accordingly, any deposition or growth methods described in connection with either layer 32 or 26, may be employed to deposit layer 38.

FIG. 7 is a high resolution Transmission Electron Micrograph (TEM) of semiconductor material manufactured in accordance with the embodiment of the invention illustrated in FIG. 3. In Accordance with this embodiment, a single crystal SrTi03 accommodating buffer layer was grown epitaxially on silicon substrate 22. During this growth process, an amorphous interfacial layer forms as described above. Next, GaAs layer 38 is formed above the accommodating buffer layer and the accommodating buffer layer is exposed to an anneal process to form amorphous oxide layer 36.

FIG. 8 illustrates an x-ray diffraction spectrum taken on a structure including GaAs compound semiconductor layer 38 and amorphous oxide layer 36 formed on silicon substrate 22. The peaks in the spectrum indicate that GaAs compound semiconductor layer 38 is single crystal and (100) orientated and the lack of peaks around 40 to 50 degrees indicates that layer 36 is amorphous.

The process described above illustrates a process for forming a semiconductor structure including a silicon substrate 22, an overlying oxide layer, and a monocrystalline gallium arsenide compound semiconductor layer 26 by the process of molecular beam epitaxy. The process can also be carried out by the process of chemical vapor deposition (CVD), metal organic chemical

vapor deposition (MOCVD), migration enhanced epitaxy (MEE), atomic layer epitaxy (ALE), physical vapor deposition (PVD), chemical solution deposition (CSD), pulsed laser deposition (PLD), or the like. Further, by a similar process, other monocrystalline accommodating buffer layers 24 such as alkaline earth metal titanates, zirconates, hafnates, tantalates, vanadates, ruthenates, and niobates, perovskite oxides such as alkaline earth metal tin-based perovskites, lanthanum aluminate, lanthanum scandium oxide, and gadolinium oxide can also be grown. Further, by a similar process such as MBE, other III-V and II-VI monocrystalline compound semiconductor layers 26 can be deposited overlying monocrystalline oxide accommodating buffer layer 24.

Each of the variations of compound semiconductor materials 26 and monocrystalline oxide accommodating buffer layer 24 uses an appropriate template 30 for initiating the growth of the compound semiconductor layer. For example, if accommodating buffer layer 24 is an alkaline earth metal zirconate, the oxide can be capped by a thin layer of zirconium.

The deposition of zirconium can be followed by the deposition of arsenic or phosphorus to react with the zirconium as a precursor to depositing indium gallium arsenide, indium aluminum arsenide, or indium phosphide respectively. Similarly, if monocrystalline oxide accommodating buffer layer 24 is an alkaline earth metal hafnate, the oxide layer can be capped by a thin layer of hafnium. The deposition of hafnium is followed by the deposition of arsenic or phosphorous to

react with the hafnium as a precursor to the growth of an indium gallium arsenide, indium aluminum arsenide, or indium phosphide layer 26, respectively. In a similar manner, strontium titanate 24 can be capped with a layer of strontium or strontium and oxygen, and barium titanate 24 can be capped with a layer of barium or barium and oxygen. Each of these depositions can be followed by the deposition of arsenic or phosphorus to react with the capping material to form a. template 30 for the deposition of a compound semiconductor material layer 26 comprising indium gallium arsenide, indium aluminum arsenide, or indium phosphide.

FIG. 9 illustrates schematically, in cross section, a device structure 50 in accordance with a further embodiment. Device structure 50 includes a monocrystalline semiconductor substrate 52, preferably a monocrystalline silicon wafer. Monocrystalline semiconductor substrate 52 includes two regions, 53 and 54. An electrical semiconductor component generally indicated by the dashed line 56 is formed, at least partially, in region 53. Electrical component 56 can be a resistor, a capacitor, an active semiconductor component such as a diode or a transistor or an integrated circuit such as a CMOS integrated circuit.

For example, electrical semiconductor component 56 can be a CMOS integrated circuit configured to perform digital signal processing or another function for which silicon integrated circuits are well suited. The electrical semiconductor component in region 53 can be formed by conventional semiconductor processing as well

known and widely practiced in the semiconductor industry. A layer of insulating material 58 such as a layer of silicon dioxide or the like may overlie electrical semiconductor component 56.

Insulating material 58 and any other layers that may have been formed or deposited during the processing of semiconductor component 56 in region 53 are removed from the surface of region 54 to provide a bare silicon surface in that region. As is well known, bare silicon surfaces are highly reactive and a native silicon oxide layer can quickly form on the bare surface. A layer of barium or barium and oxygen is deposited onto the native oxide layer on the surface of region 54 and is reacted with the oxidized surface to form a first template layer (not shown). In accordance with one embodiment, a monocrystalline oxide layer is formed overlying the template layer by a process of molecular beam epitaxy. Reactants including barium, titanium and oxygen are deposited onto the template layer to form the monocrystalline oxide layer.

Initially during the deposition the partial pressure of oxygen is kept near the minimum necessary to fully react with the barium and titanium to form monocrystalline barium titanate layer. The partial pressure of oxygen is then increased to provide an overpressure of oxygen and to allow oxygen to diffuse through the growing monocrystalline oxide layer. The oxygen diffusing through the barium titanate reacts with silicon at the surface of region 54 to form an amorphous layer of silicon oxide on second region 54 and at the interface between silicon substrate 52 and

the monocrystalline oxide. Layers 60 and 62 may be subject to an annealing process as described above in connection with FIG. 3 to form a single amorphous accommodating layer.

In accordance with an embodiment, the step of depositing the monocrystalline oxide layer is terminated by depositing a second template layer 60, which can be 1-10 monolayers of titanium, barium, barium and oxygen, or titanium and oxygen. A layer 66 of a monocrystalline compound semiconductor material is then deposited overlying second template layer 64 by a process of molecular beam epitaxy. The deposition of layer 66 is initiated by depositing a layer of arsenic onto template 64. This initial step is followed by depositing gallium and arsenic to form monocrystalline gallium arsenide 66. Alternatively, strontium can be substituted for barium in the above example.

In accordance with a further embodiment, a semiconductor component, generally indicated by a dashed line 68 is formed in compound semiconductor layer 66. Semiconductor component 68 can be formed by processing steps conventionally used in the fabrication of gallium arsenide or other III-V compound semiconductor material devices. Semiconductor component 68 can be any active or passive component, and preferably is a semiconductor laser, light emitting diode, photodetector, heterojunction bipolar transistor (HBT), high frequency MESFET, or other component that utilizes and takes advantage of the physical properties of compound semiconductor materials. A metallic conductor schematically indicated by the line 70 can be

formed to electrically couple device 68 and device 56, thus implementing an integrated device that includes at least one component formed in silicon substrate 52 and one device formed in monocrystalline compound semiconductor material layer 66. Although illustrative structure 50 has been described as a structure formed on a silicon substrate 52 and having a barium (or strontium) titanate layer 60 and a gallium arsenide layer 66, similar devices can be fabricated using other substrates, monocrystalline oxide layers and other compound semiconductor layers as described elsewhere in this disclosure.

FIG. 10 illustrates a semiconductor structure 72 in accordance with a further embodiment.

Structure 72 includes a monocrystalline semiconductor substrate 74 such as a monocrystalline silicon wafer that includes a region 75 and a region 76. An electrical component schematically illustrated by the dashed line 78 is formed in region 75 using conventional silicon device processing techniques commonly used in the semiconductor industry. Using process steps similar to those described above, a monocrystalline oxide layer 80 and an intermediate amorphous silicon oxide layer 82 are formed overlying region 76 of substrate 74. A template layer 84 and subsequently a monocrystalline semiconductor layer 86 are formed overlying monocrystalline oxide layer 80.

In accordance with a further embodiment, an additional monocrystalline oxide layer 88 is formed overlying layer 86 by process steps similar to those used to form layer 80, and an additional monocrystalline

semiconductor layer 90 is formed overlying monocrystalline oxide layer 88 by process steps similar to those used to form layer 86. In accordance with one embodiment, at least one of layers 86 and 90 are formed from a compound semiconductor material. Layers 80 and 82 may be subject to an annealing process as described above in connection with FIG. 3 to form a single amorphous accommodating layer.

A semiconductor component generally indicated by a dashed line 92 is formed at least partially in monocrystalline semiconductor layer 86. In accordance with one embodiment, semiconductor component 92 may include a field effect transistor having a gate dielectric formed, in part, by monocrystalline oxide layer 88. In addition, monocrystalline semiconductor layer 90 can be used to implement the gate electrode of that field effect transistor. In accordance with one embodiment, monocrystalline semiconductor layer 86 is formed from a group III-V compound and semiconductor component 92 is a radio frequency amplifier that takes advantage of the high mobility characteristic of group III-V component materials. In accordance with yet a further embodiment, an electrical interconnection schematically illustrated by the line 94 electrically interconnects component 78 and component 92.

Structure 72 thus integrates components that take advantage of the unique properties of the two monocrystalline semiconductor materials.

Attention is now directed to a method for forming exemplary portions of illustrative composite semiconductor structures or composite integrated

circuits like 50 or 72. In particular, the illustrative composite semiconductor structure or integrated circuit 102 shown in FIGs. 6-10 includes a compound semiconductor portion 1022, a bipolar portion 1024, and a MOS portion 1026. In FIG. 11, a p-type doped, monocrystalline silicon substrate 110 is provided having a compound semiconductor portion 1022, a bipolar portion 1024, and an MOS portion 1026.

Within bipolar portion 1024, the monocrystalline silicon substrate 110 is doped to form an N+ buried region 1102. A lightly p-type doped epitaxial monocrystalline silicon layer 1104 is then formed over the buried region 1102 and the substrate 110. A doping step is then performed to create a lightly n-type doped drift region 1117 above the N+ buried region 1102. The doping step converts the dopant type of the lightly p-type epitaxial layer within a section of the bipolar region 1024 to a lightly n-type monocrystalline silicon region. A field isolation region 1106 is then formed between the bipolar portion 1024 and the MOS portion 1026. A gate dielectric layer 1110 is formed over a portion of the epitaxial layer 1104 within MOS portion 1026, and the gate electrode 1112 is then formed over the gate dielectric layer 1110. Sidewall spacers 1115 are formed along vertical sides of the gate electrode 1112 and gate dielectric layer 1110.

A p-type dopant is introduced into the drift region 1117 to form an active or intrinsic base region 1114. An n-type, deep collector region 1108 is then formed within the bipolar portion 1024 to allow electrical connection to the buried region 1102.

Selective n-type doping is performed to form N+ doped regions 1116 and the emitter region 1120. NA doped regions 1116 are formed within layer 1104 along adjacent sides of the gate electrode 1112 and are source, drain, or source/drain regions for the MOS transistor. The N+ doped regions 1116 and emitter region 1120 have a doping concentration of at least 1E19 atoms per cubic centimeter to allow ohmic contacts to be formed. A p-type doped region is formed to create the inactive or extrinsic base region 1118 which is a P+ doped region (doping concentration of at least 1E19 atoms per, cubic centimeter).

In the embodiment described, several processing steps have been performed but are not illustrated or further described, such as the formation of well regions, threshold adjusting implants, channel punchthrough prevention implants, field punchthrough prevention implants, as well as a variety of masking layers. The formation of the device up to this point in the process is performed using conventional steps.

As illustrated, a standard N-channel MOS transistor has been formed within the MOS region 1026, and a vertical NPN bipolar transistor has been formed within the bipolar portion 1024. As of this point, no circuitry has been formed within the compound semiconductor portion 1022.

All of the layers that have been formed during the processing of the bipolar and MOS portions of the integrated circuit are now removed from the surface of compound semiconductor portion 1022. A bare silicon surface is thus provided for the subsequent

processing of this portion, for example in the manner set forth above.

An accommodating buffer layer 124 is then formed over the substrate 110 as illustrated in FIG.

12. The accommodating buffer layer will form as a monocrystalline layer over the properly prepared (i. e., having the appropriate template layer) bare silicon surface in portion 1022. The portion of layer 124 that forms over portions 1024 and 1026, however, may be polycrystalline or amorphous because it is formed over a material that is not monocrystalline, and therefore, does not nucleate monocrystalline growth. The accommodating buffer layer 124 typically is a monocrystalline metal oxide or nitride layer and typically has a thickness in a range of approximately 2-100 nanometers. In one particular embodiment, the accommodating buffer layer is approximately 5-15 nm thick. During the formation of the accommodating buffer layer, an amorphous intermediate layer 122 is formed along the uppermost silicon surfaces of the integrated circuit 102. This amorphous intermediate layer 122 typically includes an oxide of silicon and has a thickness and range of approximately 1-5 nm. In one particular embodiment, the thickness is approximately 2 nm. Following the formation of the accommodating buffer layer 124 and the amorphous intermediate layer 122, a template layer 126 is then formed and has a thickness in a range of approximately one to ten monolayers of a material. In one particular embodiment, the material includes titanium-arsenic, strontium-oxygen-arsenic, or other similar materials as

previously described with respect to FIGS. 1-5.

Layers 122 and 124 may be subject to an annealing process as described above in connection. with FIG. 3 to form a single amorphous accommodating layer.

A monocrystalline compound semiconductor layer 132 is then epitaxially grown overlying the monocrystalline portion of accommodating buffer layer 124 (or over the amorphous accommodating layer if the annealing process described above has been carried out) as shown in FIG. 13. The portion of layer 132 that is grown over portions of layer 124 that are not monocrystalline may be polycrystalline or amorphous.

The monocrystalline compound semiconductor layer can be formed by a number of methods and typically includes a material such as gallium arsenide, aluminum gallium arsenide, indium phosphide, or other compound semiconductor materials as previously mentioned. The thickness of the layer is in a range of approximately 1-5,000 nm, and more preferably 100-500 nm. In this particular embodiment, each of the elements within the template layer are also present in the accommodating buffer layer 124, the monocrystalline compound semiconductor material 132, or both.

Therefore, the delineation between the template layer 126 and its two immediately adjacent layers disappears during processing. Therefore, when a transmission electron microscopy (TEM) photograph is taken, an interface between the accommodating buffer layer 124 and the monocrystalline compound semiconductor layer 132 is seen. At this point in time, sections of the compound semiconductor layer 132 and the

accommodating buffer layer 124 (or of the amorphous accommodating layer if the annealing process described above has been carried out) are removed from portions overlying the bipolar portion 1024 and the MOS portion 1026 as shown in FIG. 14. After the section is removed, an insulating layer 142 is then formed over the substrate 110. The insulating layer 142 can include a number of materials such as oxides, nitrides, oxynitrides, low-k dielectrics, or the like. As used herein, low-k is a material having a dielectric constant no higher than approximately 3.5. After the insulating layer 142 has been deposited, it is then polished, removing portions of the insulating layer 142 that overlie monocrystalline compound semiconductor layer 132.

A transistor 144 is then formed within the monocrystalline compound semiconductor portion 1022. A gate electrode 148 is then formed on the monocrystalline compound semiconductor layer 132.

Doped regions 146 are then formed within the monocrystalline compound semiconductor layer 132. In this embodiment, the transistor 144 is a metal- semiconductor field-effect transistor (MESFET). If the MESFET is an n-type MESFET, the doped regions 146 and monocrystalline compound semiconductor layer 132 are also n-type doped. If a p-type MESFET were to be formed, then the doped regions 146 and monocrystalline compound semiconductor layer 132 would have just the opposite doping type. The heavier doped (N+) regions 146 allow ohmic contacts to be made to the monocrystalline compound semiconductor layer 132. At

this point in time, the active devices within the integrated circuit have been formed. This particular embodiment includes an n-type MESFET, a vertical NPN bipolar transistor, and a planar n-channel MOS transistor. Many other types of transistors, including P-channel MOS transistors, p-type vertical bipolar transistors, p-type MESFETs, and combinations of vertical and planar transistors, can be used. Also, other electrical components, such as resistors, capacitors, diodes, and the like, may be formed in one or more of the portions 1022,1024, and 1026.

Processing continues to form a substantially completed integrated circuit 102 as illustrated in FIG. 15. An insulating layer 152 is formed over the substrate 110. The insulating layer 152 may include an etch-stop or polish-stop region that is not illustrated in FIG. 15. A second insulating layer 154 is then formed over the first insulating layer 152. Portions of layers 154,152,142,124, and 122 are removed to define contact openings where the devices are to be interconnected. Interconnect trenches are formed within insulating layer 154 to provide the lateral connections between the contacts. As illustrated in FIG. 15, interconnect 1562 connects a source or drain region of the n-type MESFET within portion 1022 to the deep collector region 1108. of the NPN transistor within the bipolar portion 1024. The emitter region 1120 of the NPN transistor is connected to one of the doped regions 1116 of the n-channel MOS transistor within the MOS portion 1026. The other doped region 1116 is

electrically connected to other portions of the integrated circuit that are not shown.

A passivation layer 156 is formed over the interconnects 1562,1564, and 1566 and insulating layer 154. Other electrical connections are made to the transistors as illustrated as well as to other electrical or electronic components within the integrated circuit 102 but are not illustrated in the FIGs. Further, additional insulating layers and interconnects may be formed as necessary to form the proper interconnections between the various components within the integrated circuit 102.

As can be seen from the previous embodiment, active devices for both compound semiconductor and Group IV semiconductor materials can be integrated into a single integrated circuit. Because there is some difficulty in incorporating both bipolar transistors and MOS transistors within a same integrated circuit, it may be possible to move some of the components within bipolar portion into the compound semiconductor portion 1022 or the MOS portion 1024. Therefore, the requirement of special fabricating steps solely used for making a bipolar transistor can be eliminated.

Therefore, there would only be a compound semiconductor portion and a MOS portion to the integrated circuit.

In still another embodiment, an integrated circuit can be formed such that it includes an optical laser in a compound semiconductor portion and an optical interconnect (waveguide) to a MOS transistor within a Group IV semiconductor region of the same

integrated circuit. FIGs. 16-22 include illustrations of one embodiment.

FIG. 16 includes an illustration of a cross- section view of a portion of an integrated circuit 160 that includes a monocrystalline silicon wafer 161. An amorphous intermediate layer 162 and an accommodating buffer layer 164, similar to those previously described, have been formed over wafer 161. Layers 162 and 164 may be subject to an annealing process as described above in connection with FIG. 3 to form a single amorphous accommodating layer.. In this specific embodiment, the layers needed to form the optical laser will be formed first, followed by the layers needed for the MOS transistor. In FIG. 16, the lower mirror layer 166 includes alternating layers of compound semiconductor materials. For example, the first, third, and fifth films within the optical laser may include a material such as gallium arsenide, and the second, fourth, and sixth films within the lower mirror layer 166 may include aluminum gallium arsenide or vice versa. Layer 168 includes the active region that will be used for photon generation. Upper mirror layer 170 is formed in a similar manner to the lower mirror layer 166 and includes alternating films of compound semiconductor materials. In one particular embodiment, the upper mirror layer 170 may be p-type doped compound semiconductor materials, and the lower mirror layer 166 may be n-type doped compound semiconductor materials.

Another accommodating buffer layer 172, similar to the accommodating buffer layer 164, is formed over the upper mirror layer 170. In an

alternative embodiment, the accommodating buffer layers 164 and 172 may include different materials. However, their function is essentially the same in that each is used for making a transition between a compound semiconductor layer and a monocrystalline Group IV semiconductor layer. Layer 172 may be subject to an annealing process as described above in connection with FIG. 3 to form an amorphous accommodating layer. A monocrystalline Group IV semiconductor layer 174 is formed over the accommodating buffer layer 172. In one particular embodiment, the monocrystalline Group IV semiconductor layer 174 includes germanium, silicon germanium, silicon germanium carbide, or the like.

In FIG. 17, the MOS portion is processed to form electrical components within this upper monocrystalline Group IV semiconductor layer 174. As illustrated in FIG. 17, a field isolation region 171 is formed from a portion of layer 174. A gate dielectric layer 173 is formed over the layer 174, and a gate electrode 175 is formed over the gate dielectric layer 173. Doped regions 177 are source, drain, or source/drain regions for the transistor 181, as shown.

Sidewall spacers 179 are formed adjacent to the vertical sides of the gate electrode 175. Other components can be made within at least a part of layer 174. These other components include other transistors (n-channel or p-channel), capacitors, transistors, diodes, and the like.

A monocrystalline Group IV semiconductor layer is epitaxially grown over one of the doped regions 177. An upper portion 184 is P+ doped, and a

lower portion 182 remains substantially intrinsic (undoped) as illustrated in FIG. 17. The layer can be formed using a selective epitaxial process. In one embodiment, an insulating layer (not shown) is formed over the transistor 181 and the field isolation region 171. The insulating layer is patterned to define an opening that exposes one of the doped regions 177. At least initially, the selective epitaxial layer is formed without dopants. The entire selective epitaxial layer may be intrinsic, or a p-type dopant can be added near the end of the formation of the selective epitaxial layer. If the selective epitaxial layer is intrinsic, as formed, a doping step may be formed by implantation or by furnace doping. Regardless how the P+ upper portion 184 is formed, the insulating layer is then removed to form the resulting structure shown in FIG. 17.

The next set of steps is performed to define the optical laser 180 as illustrated in FIG. 18. The field isolation region 171 and the accommodating buffer layer 172 are removed over the compound semiconductor portion of the integrated circuit. Additional steps are performed to define the upper mirror layer 170 and active layer 168 of the optical laser 180. The sides of the upper mirror layer 170 and active layer 168 are substantially coterminous.

Contacts 186 and 188 are formed for making electrical contact to the upper mirror layer 170 and the lower mirror layer 166, respectively, as shown in FIG. 18. Contact 186 has an annular shape to allow

light (photons) to pass out of the upper mirror layer 170 into a subsequently formed optical waveguide.

An insulating layer 190 is then formed and patterned to define optical openings extending to the contact layer 186 and one of the doped regions 177 as shown in FIG. 19. The insulating material can be any number of different materials, including an oxide, nitride, oxynitride, low-k dielectric, or any combination thereof. After defining the openings 192, a higher refractive index material 202 is then formed within the openings to fill them and to deposit the layer over the insulating layer 190 as illustrated in FIG. 20. With respect to the higher refractive index material 202,"higher"is in relation to the material of the insulating layer 190 (i. e., material 202 has a higher refractive index compared to the insulating layer 190). Optionally, a relatively thin lower refractive index film (not shown) could be formed before forming the higher refractive index material 202. A hard mask layer 204 is then formed over the high refractive index layer 202. Portions of the hard mask layer 204, and high refractive index layer 202 are removed from portions overlying the opening and to areas closer to the sides of FIG. 15.

The balance of the formation of the optical waveguide, which is an optical interconnect, is completed as illustrated in FIG. 21. A deposition procedure (possibly a dep-etch process) is performed to effectively create sidewalls sections 212. In this embodiment, the sidewall sections 212 are made of the same material as material 202. The hard mask layer 204

is then removed, and a low refractive index layer 214 (low relative to material 202 and layer 212) is formed over the higher refractive index material 212 and 202 and exposed portions of the insulating layer 190. The dash lines in FIG. 21 illustrate the border between the high refractive index materials 202 and 212. This designation is used to identify that both are made of the same material but are formed at different times.

Processing is continued to form a substantially completed integrated circuit as illustrated in FIG. 22. A passivation layer 220 is then formed over the optical laser 180 and MOSFET transistor 181. Although not shown, other electrical or optical connections are made to the components within the integrated circuit but are not illustrated in FIG. 22. These interconnects can include other optical waveguides or may include metallic interconnects.

In other embodiments, other types of lasers can be formed. For example, another type of laser can emit light (photons) horizontally instead of vertically. If light is emitted horizontally, the MOSFET transistor could be formed within the substrate 161, and the optical waveguide would be reconfigured, so that the laser is properly coupled (optically connected) to the transistor. In one specific embodiment, the optical waveguide can include at least a portion of the accommodating buffer layer. Other configurations are possible.

Clearly, these embodiments of integrated circuits having compound semiconductor portions and

Group IV semiconductor portions, are meant to illustrate what can be done and are not intended to be exhaustive of all possibilities or to limit what can be done. There is a multiplicity of other possible combinations and embodiments. For example, the compound semiconductor portion may include light emitting diodes, photodetectors, diodes, or the like, and the Group IV semiconductor can include digital logic, memory arrays, and most structures that can be formed in conventional MOS integrated circuits. By using what is shown and described herein, it is now simpler to integrate devices that work better in compound semiconductor materials with other components that work better in Group IV semiconductor materials.

This allows a device to be shrunk, the manufacturing costs to decrease, and yield and reliability to increase.

Although not illustrated, a monocrystalline Group IV wafer can be used in forming only compound semiconductor electrical components over the wafer. In this manner, the wafer is essentially a"handle"wafer used during the fabrication of the compound semiconductor electrical components within a monocrystalline compound semiconductor layer overlying the wafer. Therefore, electrical components can be formed within III-V or II-VI semiconductor materials over a wafer of at least approximately 200 millimeters in diameter and possibly at least approximately 300 millimeters.

By the use of this type of substrate, a relatively inexpensive"handle"wafer overcomes the

fragile nature of the compound semiconductor wafers by placing them over a relatively more durable and easy to fabricate base material. Therefore, an integrated circuit can be formed such that all electrical components, and particularly all active electronic devices, can be formed within the compound semiconductor material even though the substrate itself may include a Group IV semiconductor material.

Fabrication costs for compound semiconductor devices should decrease because larger substrates can be processed more economically and more readily, compared to the relatively smaller and more fragile, conventional compound semiconductor wafers.

In accordance with the above-mentioned fabrication techniques, a ring laser gyroscope is provided, preferably on a single piece of monolithic semiconductor material. The gyroscope combines generating coherent light, ducting the light through waveguides, creating an interference pattern, and detecting said interference pattern. The invention also provides for an increase in system sensitivity by detecting the interference fringe pattern with a photodetector array, fitting the output of the array to a model of what the fringes should be, and interpolating from the model to determine a rotational parameter, such as rotational speed or angle.

In one embodiment, the interferometer is made of waveguides made of strontium titanate, barium titanate, or strontium barium titanate, of dimensions small enough in cross section so as to make the system operate in a single optical mode. The interferometer

is disposed on a substantially monocrystalline semiconductor substrate, such as silicon, upon which multiple epitaxial layers are deposited to permit the formation of active optical devices, including solid state lasers and detectors, in the manner described above.

In one embodiment, the waveguide is arranged in a square, with three corners of the square chamfered to create an optical path that is substantially lossless and turns at right angles. Metal or another highly reflective material can be coated on the corner chamfers to increase reflectivity. The waveguide can be covered with a cladding material, such as silicon dioxide, that has an index of refraction similar but less than that of the waveguide. By choosing the appropriate cladding material and/or highly reflective material, operation of the waveguide in a single optical mode is facilitated.

A beam splitter is placed in the optical path of the waveguide, regardless of the waveguides particular geometry. In the case of the square waveguide, the fourth corner includes the beam splitter. The beam splitter can be formed, for example, from an air gap between two parallel plates or by a partly metallized mirror. In addition to being optically connected to both ends of the waveguide, the beam splitter functions as a laser light input and a detector port.

A laser (e. g., edge-coupled or vertical cavity surface emitting) is preferably disposed on the surface of the substrate for generating a laser beam

that can be coupled into the waveguide after going through a beam splitter. As explained more fully below, a vertical cavity surface emitting laser could also be used with an optical interconnect to direct the laser light into the waveguide. The laser is preferably grown above a laser region of the substrate on which only epitaxial layers, if any, are grown.

This ensure that the laser is constructed on a substantially monocrystalline surface. A photodetector, which is coupled to the waveguide through the beam splitter's detector port, is also preferably disposed on the surface of the substrate for detecting an interference pattern generated at the beam splitter. Like the laser, the photodetector is preferably grown above a photodetector region of the substrate on which only epitaxial layers, if any, are grown. This ensure that the photodetector is constructed on a substantially monocrystalline surface.

During operation, the split laser beam circulates through the waveguide in opposite directions, and interferes with itself at the beam splitter. The interference pattern is then picked up by the detector. If the ring laser gyroscope is rotated in the plane of the waveguide, one beam (the beam traveling in the opposite direction of the rotation) will travel a shorter distance than the other. The difference between the two distances causes the resulting interference fringe pattern to shift.

The amount of shift depends on a number of factors. The fractional change is given by:

4-A-co fractional change = c-k where A is the planar area of the waveguide, (o is the angular velocity of the gyroscope, c is the speed of light in the waveguide, and X is the wavelength of laser light. For example, for a square gyroscopic system having a waveguide 2 cm on a side, rotating at 1000 revolution per second, using laser light having a wavelength of about 1.0 micron, the fractional shift is between about 0.25% and about 1. 0%, depending on the refractive index of the waveguide core material and precise wavelength of the laser light. This fractional shift can be increased by increasing the effective area of the interferometer by using a waveguide with multiple loops in a single plane or in multiple planes (e. g., a spiral pattern). When multiple loops are used, a connecting waveguide segment can be disposed above or below the main spiral to close the waveguide loop at the beam splitter.

An advantage of the present system is that an accurate measurement can be made by simply measuring the fractional change, i. e., the relative shift of the interference pattern--not the absolute path difference. This is because the shift can be calibrated to a particular absolute rotational speed.

This reliance on the shift of the interference pattern, rather than the pattern per se, makes this invention less sensitive to manufacturing variations.

The precision of the measurement can be improved if an array of photodetectors are used to

record an image of the actual interference pattern, which can be fit to a conventional mathematical model of the expected fringe pattern. Moreover, by integrating a microprocessor or another application- specific integrated circuit on the same substrate as the rest of the optical system, the fitting can be performed locally.

Preferred embodiments of a ring laser gyroscope semiconductor structure according to the present invention, with several variations, are shown in FIGs. 23-26. These FIGs. are not intended to show the three-dimensional geometry of the waveguides.

These FIGs. primarily show a schematic optical circuit along which laser light propagates. Thus, in each of FIGs. 23-26, laser light can be generated in the same or a different plane in which the waveguide resides.

Similarly, the detector can be located in the same or a different plane in which the waveguide and laser reside.

FIG. 23 shows an illustrative ring laser gyroscope that can be constructed according to the present invention. Ring laser gyroscope semiconductor structure 1200 at least includes: (1) semiconductor substrate 1210; (2) beam splitter region 1220, which includes beam splitting element 1230, input 1240 for receiving laser beam 1250, first optical port 1260, second optical port 1270, and detector port 1280 ; (3) waveguide 1290 that has first end 1291 and second end 1292 for optically coupling first optical port 1260 and second optical port 1270; and (4) optical detector 1295, which includes input 1296 for optically

coupling detector 1295 to waveguide detector port 1280 of beam splitter region 1220.

In a preferred embodiment, structure 1200 includes laser 1298 on substrate 1210 for providing laser beam 1250. It will be appreciated, however, that laser 1298 could be on a separate semiconductor structure, if an appropriate optical coupling between laser 1298 and beam splitter input 1240 is also provided. As discussed more fully below, laser 1298 can be any solid state laser, such as a vertical cavity surface emitting laser or an edge-coupled laser. If laser 1298 is a vertical cavity surface emitting laser, then structure 1200 preferably includes an optical interconnect disposed adjacent laser 1298 for optically coupling laser 1298 to waveguide 1290. As shown in FIGs. 16-22, an optical interconnect can be constructed using any material having a sufficiently high index of refraction to cause substantially total internal reflection of the light passing there through. In one embodiment, structure 1200 further includes integrated electronic circuitry 1299 for controlling laser 1298.

As shown more clearly in FIG. 24, beam splitter element 1230 can include a thin sheet of material that has an index of refraction that is different from the material making the rest of beam splitter region 1220. Element 1230 is positioned in the optical path of laser beam 1250 at an angle to divert first portion 1251 of beam 1250 toward first optical port 1260 and second portion 1252 of beam 1250 toward second optical port 1270. It will be appreciated that laser beam input 1240, detector port

1280, and optical ports 1260 and 1270 are not necessarily separate structures. For example, as shown in FIG. 24, those four elements merely point to locations of beam splitter region 1220 and, in this case, are integral with waveguide 1290.

Waveguide 1290 is made of a material that has an index of refraction that is different from the index of refraction of adjacent, cladding material.

Preferably, the waveguide material has an index of refraction that is greater than an index of refraction of the cladding material to facilitate operation of the waveguide in a single optical mode. Also, the waveguide preferably has dimensions in cross-section that substantially facilitate operation of the waveguide in the single optical mode. It will be appreciated that the exact dimensions can be easily determined by persons of ordinary skill in the art and depend on a number of factors, including the wavelength of the propagating light. As discussed above, the cladding material can be an oxide, a nitride, an oxynitride, a low-k dielectric, or any combination thereof. Also, the waveguide material can be, for example, strontium titanate, barium titanate, strontium barium titanate, or any combination thereof.

According to this invention, the waveguide can be in any convenient configuration, and include one or more straight segments, curved segments, or a combination of both straight and curved segments. For example, FIG. 23 shows ring laser gyroscope semiconductor structure 1200, which has four equal length segments in the shape of a square. FIGs. 25 and

26 show two additional ring laser gyroscope semiconductor structure embodiments 1300 and 1400, respectively that include curved segments.

FIG. 25 shows illustrative ring laser gyroscope structure 1300 according to the present invention. Structure 1300 includes: (1) semiconductor substrate 1310; (2) beam splitter region 1320, which includes beam splitting element 1330, input 1340 for receiving laser beam 1350, first optical port 1360, second optical port 1370, and detector port 1380; (3) waveguide 1390 that has first end 1391 and second end 1392 for optically coupling first optical port 1360 and second optical port 1370; and (4) optical detector 1395, which includes input 1396 for optically coupling detector 1395 to waveguide detector port 1380.

The main difference between structure 1200 and structure 1300 is that structure 1300 includes curved portion 1393 of waveguide 1390--structure 1200 includes waveguide 1290, but does not include such a curved portion. In both cases, however, waveguides 1290 and 1390 lie substantially in a plane that is parallel to its respective substrate surface.

Structure 1400, as shown in FIG. 26, is different from structures 1200 and 1300 because structure 1400 includes waveguide 1490, which has waveguide portions that lie in two or more planes and which is formed from multiple turns 1492,1493, and 1494. Like structures 1200 and 1300, however, ring laser gyroscope structure 1400 also includes: (1) semiconductor substrate 1410; (2) beam splitter region 1420, which includes beam splitting element

1430, input 1440 for receiving laser beam 1450, first optical port 1460, second optical port 1470, and detector port 1480 ; (3) waveguide 1490 that has first end 1491 and second end 1492 for optically coupling first optical port 1460 and second optical port 1470; and (4) optical detector 1495, which includes input 1496 for optically coupling detector 1495 to waveguide detector port 1480.

Turns 1492,'1493, and 1494 are arranged serially in a spiral pattern and lie substantially in a first plane. Segment 1496 connects an end of turn 1492 to optical port 1460. To make this connection, segment 1496 is disposed in a plane that is different from the first plane. It will be appreciated that segment 1496 can extend above or below the turns. In other words, the first plane can be located between substrate 1410 and the second plane, or the second plane can be located between the first plane and substrate 1410. In this way, first and second optical ports 1460 and 1480 can be optically coupled by the waveguide. When a waveguide segment, such as segment 1496, is formed on top of one or more other waveguide segments, a cladding material can be deposited between the segments to"planarize"the surface and to facilitate single mode waveguide operation.

It will be appreciated that two more layers of waveguides can be stacked if desired and connected as described above to further increase the effective length of the waveguide.

Detectors 1295,1395, and 1495 can be a detector array made up of a plurality of photosensitive elements arranged in at least a one dimension. Such an array provides the ability to detect and spatially resolve the position and movement of the interference pattern. These elements can also be arranged in a two dimensional array, which enables interference patterns to be stored as images for subsequent pattern and image analysis. The analysis preferably determines a rotational parameter that characterizes a rotation of the waveguide in a plane containing the waveguide, such as angular velocity o or an absolute rotational angle (e. g., by integrating o over a rotational time period).

Such analysis can be performed by an off-structure microprocessor or by a circuit that is integrated into the structure.

FIGs. 23 and 25, for example, show blocks representing integrated circuitry for performing such processing. In these cases, integrated circuits 1211 and 1311 are located substantially within their respective waveguides to conserve real estate on the substrate. The circuits can be, for example, digital signal processors (DSP). These integrated circuits, however, can also be positioned without the waveguide or even be part of another semiconductor structure or device. For example, FIG. 26 shows an alternative embodiment where circuitry 1411 is without waveguide 1490. In any case, this circuitry can be programmed to fit data generated by the photodetector to a theoretical mathematical model and the results can

be provided (electronically or optically) for subsequent data processing.

According to another aspect of this invention, illustrative methods for making ring laser gyroscopes are provided. The following fabrication methods should be read in view of the material processing techniques described above.

An illustrative method of making a ring laser gyroscope semiconductor structure is performed on a semiconductor substrate. The substrate has a surface that at least includes a laser region above which a laser can be formed and a waveguide region above which a waveguide can be formed. The method includes: (1) growing at least an accommodating layer on the substrate; (2) forming a laser on the accommodating layer above the laser region using at least one compound semiconductor material; (3) growing a high refractive index layer; (4) etching a waveguide pattern in the high refractive index layer to form a waveguide core having a longitudinal optical path; (5) cladding the waveguide core with a cladding material, wherein the cladding material has a different and lower index of refraction than the high refractive index layer; and (6) forming a beam splitter in the optical path. It will be appreciated that the order in which these steps are performed can be varied and depends on the particular design of the gyroscope being constructed.

When the laser formed is an edge-emitting laser, it has an active area that emits laser light in a plane parallel to the substrate surface. Then, the process of growing a high refractive index layer should

ensure that that layer has at least a portion that is substantially in the plane of the active area.

The formation of the accommodating layer includes growing a material having a lattice structure that substantially matched to the substrate and to the compound semiconductor material. Preferably, the accommodating material is an oxide or a nitride. The accommodating layer should be monocrystalline above the laser region and could be either monocrystalline, polycrystalline, or amorphous above the waveguide of the substrate. The accommodating layer can be used to form a waveguide core. Alternatively, an additional layer could be deposited above the accommodating layer for forming the waveguide core. As discussed fully above, a template layer can be formed between the accommodating layer and the compound semiconductor layer, if desired.

The high refractive index layer can be grown above the waveguide region on the accommodating layer, and the waveguide core is thus formed from that high refractive index layer. In any case, the waveguide core can be monocrystalline, polycrystalline, amorphous, or a combination of crystalline and amorphous. During cladding, strontium titanate, barium titanate, barium strontium titanate, an oxide, a nitride, or any combination thereof can be used as the insulting material.

A beam splitter can be formed by etching a substantially planar gap in the waveguide. The planar gap has a normal direction that is at an angle from the optical axis of the waveguide. Preferably, the gap is

formed so that the angle is about 45°. The planar gap can be filled with a spacer material. The spacer material can be the same as or different from the cladding material. If the cladding material has the same index of refraction as the spacer material, the cladding material can be used to fill the gap.

When the laser formed is a vertical cavity surface emitting laser, the step of forming the laser includes forming an active area that emits laser light along an axis that is substantially perpendicular to the substrate surface. In this case, forming the accommodating layer, etching the waveguide pattern, cladding the waveguide core, and forming the beam splitter can be before the laser is formed. The method can further include forming an optical interconnect at one end of the waveguide before the laser is formed, such that-the optical interconnect is coupled to and is at least partially below the laser. The process of etching the waveguide pattern can further include removing any high refractive index material from the accommodating layer above the laser region so that the laser can be formed thereon.

An optical interconnect can include a side wall surface that reflects laser light so that the laser is properly coupled to an end of the waveguide.

As shown throughout the FIGs., laser light can be reflected about 90°, but can also be reflected through a different angle if necessary. The side wall can be formed according to any convenient fabrication process, including"dep-etch"processing, photo-assisted etching, or preferential chemical etching.

In another embodiment according to this invention, a vertical cavity laser is coupled to a waveguide located above the laser (on the side opposite the substrate). In this case, the optical interconnect is formed after the laser. Then, growing the accommodating layer, etching the waveguide pattern, cladding the waveguide core, and forming the beam splitter preferably occur after the laser is formed.

Thus, the laser has an active area that faces away from the substrate. In this embodiment, the optical interconnect is coupled to and is at least partially "above"the laser. As described immediately above, the optical interconnect can include a side wall surface formed according to any convenient fabrication process, such as"dep-etch"processing, photo-assisted etching, or preferential chemical etching.

In a preferred embodiment, the semiconductor ring laser gyroscope structure also includes an integrated photodetector that is optically coupled to the beam splitter's detector port (as opposed to a separate photodetector device that is not integrally part of the gyroscope structure). When integrated onto the gyroscope structure, the substrate preferably has a region above which a photodetector is formed. As described above, the photodetector region may have one or more epitaxially grown layers disposed thereon. It will be appreciated, however, that according to this invention, these layers can become at least partially amorphous after they are grown epitaxially. The epitaxial growth ensures that the photodetector can be

constructed on a substantially monocrystalline surface.

Thus, a method according to this invention can further include forming a photodetector on the accommodating layer above the detector region using at least one compound semiconductor material. The waveguide is formed so that it couples the photodetector and the laser.

It will be appreciated that the method according to this invention can further include forming integrated electronic circuitry in an electronic layer as needed and in accordance with the processes outlined throughout FIGs. 1-22. Thus, the electronic layer can be the substrate surface layer, the compound semiconductor layer, another semiconductor layer, or any combination thereof. In fact, integrated electronic circuitry can be formed either above or below any other electronic and/or optical components according to this invention.

As used herein, the terms"comprises," "comprising,"or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but may also include other elements not expressly listed or inherent to such process, method, article, or apparatus.