BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a perspective view of a conventional light emitting diode (LED) chip.
FIG. 2 is a cross-sectional diagram of an LED structure according to the first embodiment of the present invention.
FIGS. 3A˜3C are perspective views of insulating layers having different shapes of openings.
FIG. 4 is a partial cross-sectional diagram illustrating the first type doped semiconductor layer, the light emitting layers, and the second type doped semiconductor layer in an LED chip according to the present invention.
FIG. 5 is a cross-sectional diagram of an LED structure according to the second embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
FIG. 2 is a cross-sectional diagram of a light emitting diode (LED) structure according to the first embodiment of the present invention. Referring to the FIG. 2, the LED structure 200 includes a substrate 210, a first type doped semiconductor layer 220, an insulating layer 230, a plurality of light emitting layers 240, a second type doped semiconductor layer 250, a first pad 260, and a second pad 270. The first type doped semiconductor layer 220 is disposed on the substrate 210. The insulating layer 230 having a plurality of openings 232 is disposed on the first type doped semiconductor layer 220 for exposing a part of the first type doped semiconductor layer 220. The light emitting layers 240 are respectively disposed within the corresponding openings 232 of the insulating layer 230. In other words, the light emitting layers 240 are disposed on a part of the first type doped semiconductor layer 220 exposed by the opening 232 of the insulating layer 230. The second type doped semiconductor layer 250 is disposed on the insulating layer 230 and the light emitting layers 240. The first pad 260 is disposed on the first type doped semiconductor layer 220 and is electrically connected to the first type doped semiconductor layer 220. The second pad 270 is disposed on the second type doped semiconductor layer 250 and is electrically connected to the second type doped semiconductor layer 250. In the present invention, the light emitting layers 240 are divided into a plurality of discrete active regions (emitting islands) by the openings 232 of the insulating layer 230, thus, the current distribution in the LED structure 200 is changed so as to increase the internal quantum efficiency, and further the light emitting efficiency of the LED structure 200.
Below, the detailed structure of the foregoing components will be described, but it should be understood that the following description is not for limiting the present invention and those skilled in the art should be able to make various changes in form and details without departing from the spirit and scope of the present invention.
The material of the substrate 210 is semiconductive or non-semiconducting material such as silicon, glass, GaAs, GaN, AlGaAs, GaP, SiC, InP, BN, Alumina, or AlN. The first type doped semiconductor layer 220 is disposed on the substrate 210, and in an embodiment of the present invention, the first type doped semiconductor layer 220 may be, for example, an n-type semiconductor layer.
The insulating layer 230 having a plurality of openings 232 is disposed on the first type doped semiconductor layer 220 for exposing a part of the first type doped semiconductor layer 220. In an embodiment of the present invention, the insulating layer 230 can be formed by insulating material such as silicon dioxide. Besides, the foregoing openings 232 may have different shapes, such as polygon, round, oval, or other shapes. FIGS. 3A˜3C are perspective views of insulating layers having different shapes of openings. Referring to FIG. 3A, the insulating layer 230 has a plurality of strip-shaped openings 232a parallel to each other; the insulating layer 230 in FIG. 3B has a plurality of rectangular openings 232b arranged in an array; and the insulating layer 230 in FIG. 3C has a plurality of oval openings 232c arranged in an array. The shape, number, and arrangement of the openings 232 of the insulating layer 230 can be designed according to different application requirement and are not limited in the present invention.
The light emitting layers 240 are respectively disposed within the openings 232 of the insulating layer 230 and are divided into a plurality of discrete emitting islands separated from each other by the openings 232 of the insulating layer 230, so that the light emitting layers 240 form a discontinuous structure. Therefore, the internal quantum efficiency of the LED structure 200 is increased. In an embodiment of the present invention, each of the light emitting layers 240 may be, for example, a GaN/InGaN multiple quantum well (MQW) structure. Besides, a part of the first type doped semiconductor layer 220 that is not covered by the insulating layer 230 and the light emitting layers 240. The second type doped semiconductor layer 250 is disposed on the insulating layer 230 and the light emitting layers 240. The second type doped semiconductor layer 250 may be, for example, a p-type semiconductor layer.
FIG. 4 is a partial cross-sectional diagram illustrating the first type doped semiconductor layer, the light emitting layers, and the second type doped semiconductor layer in an LED chip according to the present invention. Referring to FIG. 4, in an embodiment of the present invention, the first type doped semiconductor layer 220 includes, for example, a buffer layer 222, a first contact layer 224, and a first cladding layer 226. The buffer layer 222 is disposed on the substrate 210, the first contact layer 224 is disposed on the buffer layer 222, and the first cladding layer 226 is disposed on the first contact layer 224. The first cladding layer 226 can be formed by N-doped GaN. The insulating layer 230 and the light emitting layers 230 are disposed on the first cladding layer 226. The second type doped semiconductor layer 250 includes a second cladding layer 252 and a second contact layer 254. The second cladding layer 252 is disposed on the insulating layer 230 and the light emitting layers 230. The second cladding layer 252 can be formed by P-doped GaN. The second contact layer 254 is disposed on the second cladding layer 252. The second contact layer 254 can be formed by P-doped GaN.
Referring to FIG. 2 again, the first pad 260 is disposed on the part of the first type doped semiconductor layer 220 that is not covered by the insulating layer 230 and the light emitting layers 240 and is electrically connected to the first type doped semiconductor layer 220. In an embodiment of the present invention, the material of the first pad 260 may be titanium/aluminum alloy etc. The second pad 270 is disposed on the second type doped semiconductor layer and is electrically connected to the second type doped semiconductor layer 250. Besides, the material of the second pad 270 includes N-type transparent conductive oxide and P-type transparent conductive oxide. The material of the N-type transparent conductive oxide may be ITO, and the material of the P-type transparent conductive oxide is CuAlO2 etc.
FIG. 5 is a cross-sectional diagram of an LED structure according to the second embodiment of the present invention. Referring to FIG. 5, the LED structure 200′ is similar to the LED structure 200 in FIG. 2. In the present embodiment, there are air gaps 280 between the light emitting layers 240, which mean air gaps are used in the second embodiment for separating the light emitting layers 240. This structure can increase the light emitting efficiency of the LED structure 200′ as well.
To fabricate the LED structure 200′, a plurality of spacers separated from each other are formed on the first type doped semiconductor layer 220 first. Next, the light emitting layers 240 are formed between the spacers. Thereafter, the spacers are removed to form air gaps such that a plurality of light emitting layers 240 separated from each other are formed. Besides, the light emitting layers 240 in FIG. 5 can also be formed with other methods, for example, selective epitaxy. The fabrication method of the light emitting layers 240 in FIG. 5 is not limited in the present invention.
In overview, according to the LED structure of the present invention, an insulating layer having a plurality of openings is used for separating the light emitting layer into a plurality of discrete emitting islands, or air gaps are used for separating the light emitting layers, so as to increase the internal quantum efficiency of the LED structure and further to enhance the light emitting efficiency of the LED structure. In addition, the LED structure of the present invention can avoid blue shift effect through the discrete light emitting layers.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Patent Application
20080079013
