This application claims the priority benefit of Taiwan application serial no. 100117040, filed May 16, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Field of the Invention
The invention relates to a light emitting diode (LED) substrate. Particularly, the invention relates to a LED substrate having high light extraction efficiency and an LED using the same.
2. Description of Related Art
LED is a light-emitting device fabricated by a compound semiconductor, in which electric energy can be converted into light through combination of electrons and holes. The LED is belonged to a cold light source, and has advantages of low power consumption, none warm up time, long service life and fast response speed, etc., and further has features of high impact resistance and suitable for mass production, and consequently it is easy to meet application requirements to fabricate extremely small or array devices.
In order to expand the application range and future of the LED, it is one of the research focuses to improve a light-emitting brightness of the LED. In an ideal LED, after carriers in an active region are recombined into photons, if these photons can all be propagated to external, the light emitting efficiency of such LED is 100%. However, the photons generated in the active region cannot be propagated to external by 100% due to various depletion mechanisms.
In order to improve the light-emitting efficiency of the LED, a patterned LED substrate, for example, the LED substrate formed by a plurality of cones or platform structures is used to scatter the light emitted from the LED, so as to reduce a total reflection.
The invention is directed to a light emitting diode (LED) substrate, which has high light emitting efficiency.
The invention also provides a LED, which uses the aforementioned LED substrate.
The invention provides a LED substrate, which includes a sapphire substrate having a surface consisting of a plurality of upper trigonal and lower hexagonal tapers, wherein each of the upper trigonal and lower hexagonal tapers is consisted of a hexagonal taper and a trigonal taper on the hexagonal taper, and a pitch of the upper trigonal and lower hexagonal tapers is less than 10 μm.
In an embodiment of the invention, the pitch of the upper trigonal and lower hexagonal tapers has a ranging from 1 μm to 4 μm.
In an embodiment of the invention, a maximum height of each of the upper trigonal and lower hexagonal tapers has a ranging from 1 μm to which is preferably from 1.5 μm to 2 μm.
In an embodiment of the invention, a top of the trigonal taper is a plane or a pointed end.
In an embodiment of the invention, a symmetric cross-section of the trigonal taper has a first base angle and a second base angle, the second base angle is greater than the first base angle, and the second base angle is between 28 degrees and 32 degrees.
In an embodiment of the invention, a symmetric cross-section of the hexagonal taper with the trigonal taper thereon has a third base angle and a fourth base angle, wherein the fourth base angle is greater than the third base angle, and the fourth base angle is between 50 degrees and 70 degrees.
In an embodiment of the invention, the surface of the sapphire substrate includes a (0001) surface, and an area of the (0001) surface is about 10-60% of a projected area of the surface of the sapphire substrate, which is preferably 10-30%.
The invention further provides a LED including the aforementioned sapphire substrate, a first semiconductor layer stacked overlaying the sapphire substrate, a light emitting layer stacked overlaying the first semiconductor layer, a second semiconductor layer stacked overlaying the light emitting layer, a first ohmic electrode contacting the first semiconductor layer and a second ohmic electrode contacting the second semiconductor layer.
In an embodiment of the invention, the first semiconductor layer, the light emitting layer and the second semiconductor layer include a III-V semiconductor, for example, a gallium nitride semiconductor.
In an embodiment of the invention, the first and the second ohmic electrodes are respectively at least one alloy or a multi-layer film selected from the group consisting of Ni, Pb, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Ag, oxides thereof, and nitrides thereof.
In an embodiment of the invention, the first and the second ohmic electrodes are respectively an alloy or a multi-layer film selected from the group consisting of Rh, Ir, Ag and Al.
According to the above disclosure, the sapphire substrate has a light emitting surface consisted of a plurality of upper trigonal and lower hexagonal tapers, and nine surfaces of the upper trigonal and lower hexagonal taper can be used to scatter the light, so as to improve the light emitting efficiency of the substrate.
In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below.
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.
In
Referring to
Two experimental examples for manufacturing the LED substrate of the first embodiment are provided below.
First, a sapphire substrate 300 is provided, and then a hard mask 302 with a pattern is formed on the sapphire substrate 300, as that shown in
Then, a wet etching process of about several minutes is performed. During the etching process, the sapphire substrate 300 is first formed with protrusion patterns 304 of a hexagonal taper array, as that shown in
After the hard mask 302 is etched to form hexagonal tapers 306, an etching fluid continually etches the sapphire substrate 300 to form trigonal tapers 308 on the hexagonal tapers 306 as shown in
As time goes on, the height of the hexagonal tapers 306 is gradually decreased until the hexagonal tapers 306 disappear, so that an etching stop time is controlled to ensure that the sapphire substrate 300 is formed with upper trigonal and lower hexagonal tapers consisted of the hexagonal tapers 306 and trigonal tapers 310. In
Moreover, after the process shown in
Experimental examples of manufacturing the LED substrate of the invention are described as above, though the above processes are not used to limit the invention, and those skilled in the art can fabricate the structure of the invention through existing techniques according to the above descriptions.
In order to verify the effect of the LED substrate of the above embodiment, light emitting efficiencies of the LED of
First, it is assumed that the first semiconductor layer 600 is n-GaN, the light emitting layer 602 is a multiple quantum well (MQW) structure, and the second semiconductor layer 604 is p-GaN. Three types of the LED substrates including a substrate consisted of the conventional cones of
According to a simulation result, it is known that a light emitting efficiency of
In summary, in the LED substrate of in the invention, the sapphire substrate consisted of a plurality of the upper trigonal and lower hexagonal tapers serves as a light emitting surface, and the upper trigonal and lower hexagonal taper form a nine surfaces can be used to scatter the light. Therefore, the light emitting efficiency of the LED using the LED substrate of the invention is improved.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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100117040 | May 2011 | TW | national |