DEVICE AND FABRICATION

THEREOF

Field of Invention

The present invention relates to a stacked light-emitting device, in

particular, to a stacked light-emitting device having two sets of light-

emitting diode layers separately on each face of its substrate, emitting light

of similar or different colors.

Technical Background

Light-emitting diodes are made from compound semiconductor

materials and are made for the purpose of converting electricity into light.

Owing to the difference in energy band gap of the semiconductor

materials, the light-emitting devices can be made to emit visible light, such

as, red, orange, yellow, green, blue and purple color, as well as invisible

lights, such as, infrared and ultraviolet. The semiconductor materials

suitable for making high brightness light-emitting diodes are AlGaAs,

AlGaInP and InGaN.

AlGaAs has long been used to make high-brightness red and infrared

light-emitting devices. The fabrication technique of these devices involves

the use of liquid phase epitaxy (LPE). Double heterostracture (DH) layer

structure is employed to achieve high output efficiency. For high-

and yellow green light-emitting devices,

AIGaInP is the material of choice. The fabrication technique of these

devices involves the use of Metal-Organic Chemical Vapor Deposition

(MOCVD) to achieve high quality and high output. The layer structure of

the device is based on quantum well (QW) configuration to achieve higher

light output.

For high-brightness green, blue, violet and ultraviolet light-emitting

devices, InGaN is the most suitable material to use. For mass-production

of these devices, MOCVD is the most commonly used growth technique

utilized. To achieve high luminous efficacy, multi-quantum well

configuration is normally incorporated into these device structures.

The conventional method of fabricating light-emitting devices having

light of different colors, is to assemble together light-emitting device chips

emitting different colors into an aggregate. This normally takes more

module package space and is also costly from a fabrication cost viewpoint.

Summary of the Invention

This invention comprises forming light-emitting device layers on both

faces of the substrate, according to the need for light of a specific color.

By stacking the sets of light-emitting diode layers in a vertical alignment,

both the package module space and the fabrication cost can be reduced

and the effect of the light-mixing can be significantly enhanced.

of the present invention to provide a light-

emitting device having a transparent substrate with two sets of light-

emitting device layers formed separately on each of its two faces. These

two sets of light-emitting device layers can be made to emit light either

with the same or different color by varying the composition and structure

of each set of device layers. Resulting from mixing the light of the same

color, emitted simultaneously by each set of device layers, a light of the

same color with enhanced intensity is produced. Resulting from mixing

the light of different colors emitted simultaneously by each set of device

layers, a light of a third color is produced. These two sets of light-emitting

device layers can also be programmed to emit light in sequence, resulting

in light of three different colors produced in sequence.

The techniques for forming the light-emitting device layers on each

face of the transparent substrate involve bonding by ultrasonic fusion,

transparent adhesives, such as epoxy, silicone or other related bonding

techniques. The transparent substrate can be made of sapphire, glass or

other transparent materials. The two sets of light-emitting device layers

can be made of quaternary epilayers at the bottom with quaternary

epilayers at the top, binary epilayers at the bottom with binary epilayers at

the top or quaternary epilayers at the bottom with binary epilayers at the

top. The combination of two sets of device epilayers can be adjusted

ήedd ^' -offfie color. For instance, red device layers at the

top with green device layers at the bottom produces white light; blue

device layers at the top with yellow device layers at the bottom also

produces white light.

The technique for electrically connecting the light-emitting device

layers on each face of the transparent substrate, involve either wire-

bonding or flip-chip bonding. It is also possible to form device layers in

different forms, such as rectangular, circular, square, etc. A single set of

light emitting layers may be formed on each surface of the substrate or an

array of sets may be formed on each surface.

The advantages of the present invention can be realized in terms of

fabrication cost, as well as performance. By stacking sets of device layers

having similar or different compositions and structures in vertical fashion,

the module package space can be reduced and the fabrication process can

also be simplified. In addition, the mixing effect of light with either

similar or different colors can be enhanced.

Brief Description of the Drawings

These and other features and advantages of the present invention will

become better understood by reference to the following detailed

description, when considered in connection with the accompanying

drawings, wherein:

FIGT Migrates the" Wst embodiment employing the principles of the

present invention.

FIG 2 illustrates the second embodiment employing the principles of

the present invention.

FIG 3 illustrates the third embodiment employing the principles of the

present invention.

FIG 4 illustrates the fourth embodiment employing the principles of the

present invention.

Referring now to FIG 1 though FIG 4, 1 refers to yellow LED

epilayers, 2 refers to a joining interface (a set of epilayers join with the

transparent substrate), 3 refers to a transparent substrate, 4 refers to blue

epilayers, 5 refers to light of yellow color, 6 refers to light of blue color, 7

refers to light of white color, 8 refers to epilayers of infrared light, 9 refers

to epilayers of green light, 10 refers to light of red color, 11 refers to light

of green color.

Description of the Preferred Embodiment

The present invention comprises a stacked light-emitting device. The

first embodiment, employing the principles of the present invention, is

illustrated in FIG 1, consisting of two yellow light-emitting device

epilayers 1, a joining interface 2, a transparent substrate 3, two blue light-

emitting device epilayers emitting blue light 4, yellow light 5, blue light 6,

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The light emitting device further comprises cathode electrodes 20, 21,

anode electrodes 22, 34 and bonding wires 23, 24, which provide electrical

connection to electrodes 25, 26. The light-emitting device sits on bumps

27, 28 which are placed on metal electrodes 29, 30, placed on submount

31 for electrical connection purposes. These same items are also present

in the embodiments of Figs. 2, 3, and 4, but are only numbered in Fig. 1.

Blue light 6 is emitted from active light emitting layer 32 and yellow

light is emitted from active light emitting layer 33.

The fabrication technique of the present invention involves first the

growth of InGaN-based blue light-emitting device epilayers 4 epitaxially

grown on the top surface of a transparent substrate 3 (sapphire). Secondly,

AlGalnP-based yellow light-emitting device epilayers 1 are then adhered

onto the bottom surface of transparent substrate 3 using a transparent

adhesive material (epoxy) as a joining interface 2. Through the mixing of

yellow light 5 and blue light 6, white light 7 is thus produced.

The second embodiment employing the principles of the present

invention, illustrated in FIG 2, involves the growth of InGaN-based green

light-emitting device epilayers 9 grown on the top surface of a transparent

substrate 3 (sapphire). Red light-emitting device epilayers 8 are then

adhered onto the bottom surface of transparent substrate 3 by a transparent

a joining interface 2. Through the mixing of

red light 10 and green light 11, white light is also thus produced.

The third embodiment employing the principles of the present invention

is illustrated in FIG 3. The fabrication technique involves the growth of

InGaN-based green light-emitting device epilayers 9 on the top surface of

a transparent substrate 3 and the growth of InGaN-based green light-

emitting device epilayers 9 on the bottom surface of substrate 3. Through

the combining of the green light emitted from these two device epilayers, a

two-fold enhanced green light 11 is thus produced, which greatly improves

the low light output suffered by conventional green light-emitting devices.

The fourth embodiment employing the principles of the present

invention is illustrated in FIG 4. The fabrication technique involves the

bonding 2 of two yellow light-emitting device epilayers 1 separately onto

the top and bottom surfaces of a transparent substrate 3 (sapphire).

Through the combining of the yellow light emitted from these two device

epilayers, a two-fold enhanced yellow light 5 is thus produced which

greatly improves the low light output suffered by conventional yellow

light-emitting devices.

Having thus described the invention, we claim: