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.
FIGS. 1A to 1C are schematic, cross-sectional diagrams illustrating the process flow for fabricating a nano/micro structure according to a preferred embodiment of the present invention.
FIG. 2 is a picture of a nano/micro structure formed according to the above-mentioned processes captured by an electron-microscope.
FIG. 3 is a cross-sectional view showing an LED device according to a preferred embodiment of the present invention.
FIG. 4 is a cross-sectional view showing an LED having two roughness layers according to another preferred embodiment of the present invention.
FIG. 5 is a cross-sectional view showing an LED having three roughness layers according to another preferred embodiment of the present invention.
FIG. 6 is a diagram illustrating a relationship of wavelength and RT-PL intensity measured from the standard 400 nm LED structure and the 400 nm LED structure on the substrate having the nano/micro structure according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating a relationship of injection current and EL integrated intensity measured from the standard 400 nm LED structure and the 400 nm LED structure on the substrate having the nano/micro structure according to an embodiment of the present invention.
DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
FIGS. 1A to 1C are schematic, cross-sectional diagrams illustrating the process flow for fabricating a nano/micro structure according to a preferred embodiment of the present invention. First, referring to FIG. 1A, a film 110 is provided. In one embodiment of the present invention, the film 110 may be the LED substrate, such as the sapphire substrate, or one of the films of the LED device, such as the N-type doped semiconductor layer, the P-type doped semiconductor layer or the transparent conductive layer to be roughed.
Then, please refer to FIG. 1B, a mixed material 120 is formed on the film 110, and the mixed material 120 comprises a plurality of particles 122 and a filler 124 among the particles 122. In this embodiment, the particles 122 and the filler 124 in liquid phase are mixed together in advance, and then a layer of the filler 124 and the particles 122 distributed therein is coated onto the film 110 by spinning coating. Basically, the mixed material 120 having the particles 122 has formed a nano/micro structure with a convex surface. However, if a nano/micro structure with a concave surface is desired, the user may need to proceed with the following step. By controlling a rotation speed of the spinning coating process, the particles 122 may be periodically arranged in a mono-layer on the film 110. Besides, the particles 122 may be arranged in two or more layers according to the concentration of the mixed solution coated on the film 110 and/or the rotation speed; however the number of the layers is not limited in the present invention. Except spinning coating, the mixed material 120 can be formed on the film 110 by dip coating, natural drying or other suitable method. The particles 122 may be in contact with the neighboring particles, or otherwise separated from each other as shown in FIG. 1B. In one embodiment of the present invention, the particles 122 may comprise a plurality of micro-scaled particles, a plurality of nano-scaled particles, or a mixture of the micro-scaled particles and the nano-scaled particles. The particles 122 may be made of polymer, metal or metal oxide. For example, the material of the polymer comprises polymethylmethacrylate (PMMA), polystyrene (PS) and so on; the material of the metal comprises gold, silver, copper, Ni, Ti, Al and the like; the material of the metal oxide comprises silicon dioxide, titanium dioxide and the like. Besides, a material of the filler 124 comprises an inorganic material, and the inorganic material may be metal alkoxides, metal oxide precursor or a plurality of metal particles.
Finally, please refer to FIG. 1C, the particles 122 are removed, such that a plurality of highly-ordered concaves 124a is formed on the surface of the filler 124, which serves as a nano/micro structure on the film 110. The size of the concaves 124a may be changed according to the diameter of the particles 122. Besides, according to an embodiment of the present invention, the particles 122 can be removed by the etching process, the solvent extraction process, the thermal treatment process or other suitable process. Thus far, the nano/micro structure on the film 110 is formed according to the above processes.
FIG. 2 is a picture of a nano/micro structure on a film formed according to the above-mentioned processes captured by an electron-microscope. The fabrication process of the nano/micro structure on the film comprises the following steps. First, a mixture of the micro-scaled styrene particles and the solution having aluminium particles is coated on the sapphire substrate. Then, the micro-scaled styrene particles are removed, such that a nano/micro structure, which is comprised of aluminium oxide and has a plurality of micro-scaled concaves, is formed on the sapphire substrate.
The fabrication of the nano/micro structure may be applied to any kinds of the light emitting devices for enhancing the light emitting efficiency thereof. In the present invention, the fabrication of the nano/micro structure is applied to one or more of the films of the LED device in order to avoid the occurrence of the total internal reflection. The LED devices having the nano/micro structure on one or more of the films are illustrated as follows.
FIG. 3 is a cross-sectional view showing an LED device according to a preferred embodiment of the present invention. Referring to FIG. 3, the LED 200 mainly comprises a substrate 210, a first roughness layer 220, a first type doped semiconductor layer 230, a light emitting layer 240, a second type doped semiconductor layer 250, a transparent conductive layer 260, a first electrode 270 and a second electrode 280. The first roughness layer 220 having a plurality of micro-scaled or nano-scaled concaves 222 is adapted to enhance the extraction efficiency of the LED 200 and is formed on the substrate 210 according to the above-mentioned processes. Furthermore, a material of the first roughness layer 220 depends on that of the precursor, and therefore the material of the first roughness layer 220 may be the same or different from that of the substrate 210. Then, an active layer constructed by the first type doped semiconductor layer 230, the light emitting layer 240 and the second type doped semiconductor layer 250 is formed, for example but not limited to, by performing a series of epitaxy processes sequentially on the first roughness layer 220. In this embodiment, the first type doped semiconductor layer 230 is an N-type doped semiconductor layer, and the second type doped semiconductor layer 250 is a P-type N-type doped semiconductor layer.
Moreover, in the succeeding process, a portion of the first type doped semiconductor layer 230, a portion of the light emitting layer 240 and a portion of the second type doped semiconductor layer 250 are removed, for example but not limited to, by etching or by another method, to form an isolated island structure (MESA). Then, the transparent conductive layer 260 is formed on the second type doped semiconductor layer 250. Finally, the first electrode 270 is formed on the exposed first type doped semiconductor layer 230, and the second electrode 280 electrically isolated from the first electrode 270 is formed on the transparent conductive layer 260. Since the surface of the substrate 210 is roughed by the fabrication of the first roughness layer 220, which does not require the etching process, therefore, the fabrication time and cost of the LED device can be reduced.
The substrate 210 may be a glass substrate, a silicon substrate, a sapphire substrate or the like. A material of the first roughness layer 220 comprises an inorganic material, such as metal alkoxides, metal oxide precursor or a plurality of metal particles. A material of the first type doped semiconductor layer 230 and the second type doped semiconductor layer 250 comprises a III-V group compound of semiconductor material, such as a gallium nitride (GaN), a gallium phosphide (GaP) or a gallium phosphide arsenide (GaAsP). The light emitting layer 240 may comprise a single or a multi quantum well structure, to enhance the light emitting efficiency. Besides, a material of the transparent conductive layer 260 preferably comprises an indium tin oxide (ITO), but also may comprise, for example but not limited to, such as indium tin oxide, cadmium tin oxide, ZnO:Al, ZnGa2O4, SnO2:Sb, Ga2O3:Sn, AgInO2:Sn, In2O3:Zn, NiO, MnO, FeO, Fe2O3, CoO, CrO, Cr2O3, CrO2, CuO, SnO, Ag2O, CuAlO2, SrCu2O2, LaMnO3, PdO or the like. The first electrode 270 can be made of a metallic alloy including Ti/Al, Ti/Al/Ti/Au, Ti/Al/Pt/Au, Ti/Al/Ni/Au, Ti/Al/Pd/Au, Ti/Al/Cr/Au, Ti/Al/Co/Au, Cr/Al/Cr/Au, Cr/Al/Pt/Au, Cr/Al/Pd/Au, Cr/Al/Ti/Au, Cr/Al/Co/Au, Cr/Al/Ni/Au, Pd/Al/Ti/Au, Pd/Al/Pt/Au, Pd/Al/Ni/Au, Pd/Al/Pd/Au, Pd/Al/Cr/Au, Pd/Al/Co/Au, Nd/Al/Pt/Au, Nd/Al/Ti/Au, Nd/Al/Ni/Au, Nd/Al/Cr/Au, Nd/Al/Co/A, Hf/Al/Ti/Au, Hf/Al/t/Au, Hf/Al/Ni/Au, Hf/Al/Pd/Au, Hf/Al/Cr/Au, Hf/Al/Co/Au, Zr/Al/Ti/Au, Zr/Al/Pt/Au, Zr/Al/Ni/Au, Zr/Al/Pd/Au, Zr/Al/Cr/Au, Zr/Al/Co/Au, TiNx/Ti/Au, TiNx/Pt/Au, TiNx/Ni/Au, TiNx/Pd/Au, TiNx/Cr/Au, TiNx/Co/Au TiWNx/Ti/Au, TiWNx/Pt/Au, TiWNx/Ni/Au, TiWNx/Pd/Au, TiWNx/Cr/Au, TiWNx/Co/Au, NiAl/Pt/Au, NiAl/Cr/Au, NiAl/Ni/Au, NiAl/Ti/Au, Ti/NiAl/Pt/Au, Ti/NiAl/Ti/Au, Ti/NiAl/Ni/Au, Ti/NiAl/Cr/Au or the like. The material of the second electrode 270 may comprise metallic alloys such as Ni/Au, Ni/Pt, Ni/Pd, Ni/Co, Pd/Au, Pt/Au, Ti/Au, Cr/Au, Sn/Au, Ta/Au, TiN, TiWNx, WSix or the like.
Besides, the roughness layer may be formed on one or more of the films of the LED to further enhance the extraction efficiency of the LED, and the number and position of the roughness layers are not limited in the present invention. The LED devices having two or more roughness layers are illustrated in the following.
FIG. 4 is a cross-sectional view showing an LED having two roughness layers according to another preferred embodiment of the present invention. Please refer to FIG. 4, the structure of the LED 200′ is similar to that of the LED 200 shown in FIG. 3, and the difference between them lies in that the LED 200′ further comprises a second roughness layer 220′ disposed on the first type doped semiconductor layer 230. The structure and material of the second roughness layer 220′ are the same as those of the first roughness layer 220, and therefore it is not repeated herein.
FIG. 5 is a cross-sectional view showing an LED having three roughness layers according to another preferred embodiment of the present invention. Please refer to FIG. 5, the structure of the LED 200″ is similar to that of the LED 200′ shown in FIG. 4, and the difference between them lies in that the LED 200″ further comprises a third roughness layer 220″ disposed on the transparent conductive layer 260. The structure and material of the third roughness layer 220″ are the same as those of the first roughness layer 220, and therefore it is not repeated herein.
FIG. 6 is a diagram illustrating a relationship of wavelength and RT-PL intensity measured from the standard 400 nm LED structure and the 400 nm LED structure on the substrate having the nano/micro structure according to an embodiment of the present invention. FIG. 7 is a diagram illustrating a relationship of injection current and EL integrated intensity measured from the standard 400 nm LED structure and the 400 nm LED structure on the substrate having the nano/micro structure according to an embodiment of the present invention. It is clear from FIGS. 6 and 7, compared with the standard 400 nm LED structure, the RT-PL intensity and EL integrated intensity of the 400 nm LED structure on the substrate having the nano/micro structure are improved.
In summary, the present invention is to form a mixed material comprising a plurality of particles and the filler among the particles on the film. Then, the particles are removed by the etching process, the solvent extraction process or the thermal treatment process, such that the micro-scaled or nano-scaled concaves are formed on the surface of the filler, which serves as the nano/micro structure of the film. The fabrication of the nano/micro structure may be applied to one or more of the films of the LED device to be roughed, such that the extraction efficiency of the LED device may be enhanced. Compared with the etching process, the fabrication method of the present invention may reduce the fabrication time and cost effectively, thus increasing the productivity of the LED device.
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.