SEMICONDUCTOR EMITTING LIGHT AND METHOD FOR

MANUFACTURING SEMICONDUCTOR EMITTING LIGHT Technical Field [1] The present invention relates to a semiconductor light emitting diode whose driving voltage is reduced and whose optical efficiency is improved and a method of manu¬ facturing the same. Background Art [2] In general, light emitting diodes (LED) are a kind of semiconductor for converting electricity into ultraviolet rays or light using the characteristic of compound semi¬ conductor to transmit and receive signals and are used for electric home appliances, remote controllers, electric signs, displays, and various automatic devices. [3] When forward voltage is applied to semiconductor of a specific element, electrons and holes are transmitted through positive-negative junction parts to be re-combined with each other. At this time, energy level becomes lower due to the combination of electrons and holes so that the energy level is emitted as light. [4] Also, the LED is commonly made small and is mounted in an epoxy mold, a lead frame, and a printed circuit board (PCB). The most commonly used LED is 5mm (T 1 3/4) plastic package. However, a new type of package is developed in accordance with a specific application field. Wavelengths are created by the combinations of the elements that constitute a semiconductor chip to determine the colors of the light emitted from the LED. [5] In particular, according as information and communication devices are small and slim, resistors, condensers, and noise filters that are various parts of the devices are made smaller. In order to directly mount the LED on a PCB substrate, the LED is made as a surface mount device (SMD). [6] Therefore, an LED lamp used as a display is developed as the SMD. The SMD can replace a conventional simple illuminating lamp and is used as an illumination display, a character display, and an image display that display various colors. [7] Recently, according as high density integration technology with respect to semi¬ conductor devices has been developed and consumers prefer compact electronic products, a surface mount technology (SMT) is widely used and a technology of minimizing an installation space such as ball grid array (BGA), wire bonding, and flip chip bonding is adopted as a technology of packing a semiconductor device. [8] FIG. 1 illustrates processes of manufacturing a conventional semiconductor LED. [9] As illustrated in FIG. 1, a GaN buffer layer 11 is formed on a sapphire substrate 10 formed of an A12O3 based component. Then, an undoped GaN layer 13 is con¬ tinuously grown on the buffer layer 11. [10] As described above, in order to thin film grow a three group based element on the sapphire substrate 10, a metal organic chemical vapor deposition (MOCVD) method is commonly used and growth pressure is maintained to be 200 to 650 torr to form a layer. [11] An n-type GaN layer 14 is formed of silicon using Si:H4 or Si2H6 gas on the undoped GaN layer 13. [12] When the n-type GaN layer 14 is grown, an activation layer 15 is grown on the n- type GaN layer 14. The activation layer 15 as an emission region is a semiconductor layer to which luminescent material formed of InGaN is added. When the activation layer 15 is grown, a p-type AlGaN(Mg) layer 16 is continuously formed. Here, the Mg based two group element is used as the p-type AlGaN(Mg) layer 16. [13] The p-type AlGaN(Mg) layer 16 is contrary to the n-type GaN layer 14 that supplies electrons to the activation layer 15 by voltage applied from the outside. [14] The p-type AlGaN(Mg) layer 16 supplies holes to the activation layer 15 by the voltage applied from the outside to combine the holes and electrons with each other in the activation layer 15 to emit light. [15] A p-type GaN layer 17 is grown on the p-type AlGaN(Mg) layer 16 to electrically contact a p-type electrode 20 to be formed later. The edges of the p-type GaN layer 17, the p-type AlGaN(Mg) layer 16, the activation layer 15, and the n-type GaN layer 14 are etched to electrically contact an n-type electrode 30 and the undoped GaN layer 13. The undoped GaN layer 13 is exposed . [16] Then, the n-type electrode 30 is formed on the exposed undoped GaN layer 13 and the p-type electrode 20 is formed on the p-type GaN layer 17. [17] However, the p-type GaN layer 17, the p-type AlGaN(Mg) layer 16, and the activation layer 15 sense vertical resistance of 0.3μm from the p-type electrode 20 and the activation layer 15 senses vertical resistance of several tens to several hundreds μm from the n-type electrode 30. [18] That is, the electrons transmitted from the n-type electrode 30 have larger transmission distance than the holes transmitted from the p-type electrode 20 so that the activation layer 15 senses higher resistance from the n-type electrode 30. [19] When the size of the LED package is 200μm*200μm, the area through which current flows by the holes is about 170μm*170μm and the area through which current flows by the electrons is about 200μm*4μm when it is assumed that the thickness of an n-type contact layer is 4μm so that the area of electron current is smaller than the area of hole current about 50 times. [20] Therefore, although the resistivity of the undoped GaN layer 13 is smaller than the resistivity of the p-type GaN layer 17 no less than 100 times, the resistance that the n- type electrode 30 senses from the undoped GaN layer 13 is larger than the resistance that the n-type electrode 30 senses from the p-type GaN layer 17 several tens times. [21] The resistance is no less than 10Ω and occupies a larger part than dynamic resistance. Therefore, in order to reduce the resistivity of the p-type GaN layer 17, doping must be increased to increase the density of electrons. [22] At this time, Mg is used so that it is difficult to increase the density of electrons no less than 1*1018cm" and, even if the density of electrons of no less than 1*1018cm" is obtained, the crystal structure of the p-type GaN layer 17 significantly deteriorates and the surface of the p-type GaN layer 17 becomes rough. [23] As described above, in order to improve the crystallization and to reduce the re¬ sistivity of the p-type GaN layer 17 whose crystal structure deteriorates and whose surface is rough, the p-type GaN layer 17 is doped so that the density of electrons is 2 to 4* 1017cm"3. At this time, the resistivity of the p-type GaN layer 17 is about 2 to 3Ωcm. [24] Recently, a technology of reducing resistance by increasing the density of electrons of the undoped GaN layer 13 to no less than 5* 1018cm" has been devised in Japan and the United States. However, such a technology has limitations on controlling the density of holes of the p-type GaN layer 17 to reduce the resistivity of the p-type GaN layer 17. [25] Therefore, in order to maintain a layer having high crystallization and uniform flatness, it is necessary to dope a large amount of Si so that the resistance of the undoped GaN layer 13 is reduced and that the driving voltage of the LED is reduced and to uniformly implant current so that an LED capable of emitting light with high brightness is developed. Disclosure of Invention Technical Problem [26] It is an object of the present invention to provide a semiconductor LED in which a low temperature delta doped semiconductor layer is formed between the activation layer and the p-type electrode of the semiconductor LED to increase the density of electrons and the flatness of the surface of the semiconductor layer so that it is possible to reduce the driving voltage of the semiconductor LED and that the semiconductor LED can emit light with high brightness and a method of manufacturing the same. Technical Solution [27] In order to achieve the above object, there is provided a method of manufacturing a semiconductor light emitting diode, the method comprising the steps of forming a first GaN based layer, forming an activation layer on the first GaN based layer, forming a low temperature delta doping layer for increasing the density of holes on the activation layer, and forming a second GaN based layer on the low temperature delta doping layer. [28] According to another embodiment of the present invention, there is provided a semiconductor light emitting diode comprising a first GaN based layer, an activation layer formed on the first GaN based layer, a low temperature delta doping layer formed on the activation layer, and a second GaN based layer formed on the low temperature delta doping layer. [29] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Advantageous Effects [30] According to the present invention, the low temperature delta doped semiconductor layer is formed between the activation layer and the p-type electrode of the LED to increase the density of holes and the flatness of the surface of the semiconductor layer so that it is possible to reduce the driving voltage of the LED and that the LED can emit light with high brightness. Brief Description of the Drawings [31] FIG. 1 illustrates processes of manufacturing a conventional semiconductor LED. [32] FIG. 2 illustrates processes of manufacturing a semiconductor LED according to the present invention. [33] FIG. 3 is a graph illustrating the voltage-current characteristic of the semiconductor LED according to the present invention. [34] FIG. 4 is a graph illustrating the current-light intensity characteristic of the semi¬ conductor LED according to the present invention. Mode for the Invention [35] Preferred embodiments of the present invention will be described in detail with reference to the attached drawings. [36] FIG. 2 illustrates processes of manufacturing a semiconductor LED according to the present invention. [37] As illustrated in FIG. 2, a GaN buffer layer 111 is formed on a sapphire substrate 100 formed of an A12O3 based component. Then, an undoped GaN layer 113 is con¬ tinuously grown on the buffer layer 111. [38] As described above, in order to thin film grow a three group based element on the sapphire substrate 100, a metal organic chemical vapor deposition (MOCVD) method is commonly used and growth pressure is maintained to be 200 to 650 torr to form a layer. [39] An n-type GaN layer 114 is formed of silicon using Si:H4 or Si2H6 gas on the undoped GaN layer 113. [40] When the n-type GaN layer 114 is grown, an activation layer 115 is grown on the n- type GaN layer 114. The activation layer 115 as an emission region is a semiconductor layer to which luminescent material formed of InGaN is added. When the activation layer 115 is grown, a p-type low temperature delta doped layer 116 is continuously formed. [41] The p-type low temperature delta doped layer 116 is formed by a delta doping process to have high density of holes so that the LED is driven by low driving voltage with high emission efficiency. [42] In the delta doping process, when a semiconductor epitaxial layer is grown on a substrate, dopants are flown into a crystal growth chamber to form a doping layer having the thickness of an atomic layer. [43] As described above, after forming the doping layer of the thickness of the atomic layer while the epitaxial layer is grown, the epitaxial layer is continuously grown, a strong electric field caused by dopants implanted into the doping layer forms a potential well in which a charge layer of high density may be formed. [44] Also, when delta doping is performed, the solubility of the dopants exceeds the limitations on the solubility of the dopants when uniform doping is performed so that it is possible to obtain charges of high density. Also, doping is performed to a thickness of one or two atomic layers so that it is possible to prevent the crystallization of the dopants or the state of the surface of the dopants from deteriorating. [45] Since the p-type low temperature delta doping layer 116 is formed by the above- described delta doping process, the p-type low temperature delta doping layer 116 is doped with a maximum amount of Mg to increase the density of holes of the LED and to reduce the resistivity of the LED. [46] Be and Zn as well as Mg may be used as the metal with which the p-type low temperature delta doping layer 116 is doped. [47] When the p-type low temperature delta doping layer 116 is grown, delta doping is performed in a state where TMG gas source is stopped at the depth of 0.2 to 0.5nm. After the p-type low temperature delta doping layer 116 is grown, the p-type low temperature delta doping layer 116 is activated to a nitrogen atmosphere in a reaction tube to reduce the resistance of a p-type GaN layer 117. [48] Processes of forming the p-type low temperature delta doping layer 116 will be described in detail. After the activation layer 115 is grown, temperature is raised to 750 to 850°C, preferably, 850°C and the TMG gas is exhausted to the outside. [49] Then, hydrogen gas, ammonia gas, and Cp2Mg that is Mg doping source of 2*10 mol/min are flown into the reaction tube of the crystal growth chamber for 3 to 60 seconds to form an Mg delta doping layer. [50] Mg may be replaced by Be or Zn. [51] When the doping layer is formed, temperature is raised to l,010°C to form the p- type GaN layer 117 while flowing TMGa and Cp2Mg. [52] Therefore, the p-type low temperature delta doping layer 116 supplies holes to the activation layer 115 by voltage applied to the outside so that the holes and electrons are combined with each other in the activation layer 115 to emit light. [53] The p-type GaN layer 117 is grown and the edges of the p-type GaN layer 117, the p-type low temperature delta doping layer 116, the activation layer 115, and the n-type GaN layer 114 are etched to electrically contact an n-type electrode 130 and the undoped GaN layer 113 to expose the undoped GaN layer 113. [54] Then, the n-type electrode 130 is formed on the exposed undoped GaN layer 113 and the p-type electrode 120 is formed on the p-type GaN layer 117. [55] As described above, when the p-type low temperature delta doping layer 116 is formed between the activation layer 115 and the p-type GaN layer 117, solubility of dopants in semiconductor nitride exceeds the limitations on the solubility of the dopants when uniform doping is performed so that it is possible to obtain charges of high density. [56] Also, doping is performed to a thickness of one or two atomic layers so that it is possible to prevent the crystallization of the dopants or the state of the surface of the dopants from deteriorating. [57] FlG. 3 is a graph illustrating the voltage-current characteristic of the semiconductor LED according to the present invention. [58] As described in FIG. 3, the driving voltage of the LED having the low temperature delta doping layer according to the present invention and the driving voltage of the conventional LED are compared with each other. [59] As illustrated in FIG. 3, desired current is generated by the driving voltage of 3V according to the present invention, however, the driving voltage of 3.5V is required by the conventional LED. [60] The resistance value of the LED having the p-type low temperature delta doping layer in the p-type electrode region of the LED is 18Ω at the driving current of 2OmA. The resistance value of the conventional LED in the p-type electrode region of the LED is 24Ω. [61] FIG. 4 is a graph illustrating the current-light intensity characteristic of the semi¬ conductor LED according to the present invention. As illustrated in FIG. 4, when the brightness of light emitted from the semiconductor LED according to the present invention and the brightness of light emitted from the conventional LED are compared with each other, based on the same current value, the brightness of light emitted from the semiconductor LED according to the present invention is higher than the brightness of light emitted from the conventional LED. [62] This means that the p-type low temperature delta doping layer reduces the driving voltage of the LED and increases the density of holes to increase the amount of light emitted from the activation layer. [63] The low temperature delta doping layer according to the present invention reduces the driving voltage of the LED so that it is possible to reduce power consumption and to improve optical efficiency. Industrial Applicability [64] According to the present invention, there is provided a semiconductor LED in which it is possible to increase the density of holes and the flatness of the surface of the semiconductor layer so that it is possible to reduce the driving voltage of the semi¬ conductor LED and that the semiconductor LED can emit light with high brightness and a method of manufacturing the same.