Light-emitting device having patterned substrate and method of manufacturing thereof

Abstract

A light-emitting device disclosed herein comprises a patterned substrate having a plurality of cones, wherein a space is between two adjacent cones. A light-emitting stack formed on the cones. Furthermore, the cones comprise an area ratio of a top area of the cone and a bottom area of the cone which is less than 0.0064.

Description

REFERENCE TO RELATED APPLICATION

nm μm to ensure that the growth time of epitaxial layers does not take too long. In sum, the distance S between two adjacent cones 102 and the bottom width D1 of the cone 102 have a relationship represented by a first ratio Q1=S/(D1+S), wherein the ratio Q1 is about 0.01-0.3 in the embodiment. In a preferred embodiment, the distance S between two adjacent cones 102 is preferred to be 0.1-0.4 μm and the first ratio Q1 is preferred to be between 0.03-0.15.

As shown in FIG. 3, cones 102 with an arc 204 protruding from the inclined sidewall 203 enhance the light extraction because the amount of light falling on the cones 102 is increased and more light is diffused. Based on Snell's Law total internal reflection happens within the cone 102 at the intersection between the intermediate layer 103 and the cone 102 because the refractive index of the intermediate layer 103 is larger than that of the substrate 101. To sum up, due to the light diffused by the cones 102, the light extraction efficiency is increased.

As mentioned above, the larger the maximum distance B between the arc 204 and the chord 205 of the arc 204, the larger the surface area of the cone 102 for diffusing the light and increasing the light extraction efficiency. But a larger distance B can hinder the epitaxial layer from growing on the space (not shown) between two adjacent cones 102, and can increase the probability of the light being absorbed between adjacent cones 102. In one embodiment, the maximum distance B between the arc 204 and the chord 205 of the arc 204 can be 0-0.5 nm μm, and in another embodiment, it is expected to be 0-0.2 nm μm considering the growth of the epitaxial layers. Thus the spacing S between two adjacent cones 102, the maximum distance B between the arc 204 and the chord 205 of the arc 204 and the bottom width D1 of the cone 102 form a relationship represented by a second ratio Q2=B/(D1+S), which is used for preventing light absorption between adjacent cones 102 and to ensure a sufficient growth time for growing the epitaxial layers. The second ratio Q2 can be around 0-0.2, and preferably to be 0-0.05.

In order to avoid the light absorption due to the light reflection inside the cones 102 of substrate 101 caused by the difference between refractive index between the intermediate layer 103 and the substrate 101, the top width D2 of the cone 102 is expected to be larger than 0. The larger top width D2 of the cone 102 implies a larger entrance for light to emit into cones 102, while the top width D2 of the cone 102 is between 0-(Wd/n_intermediate) nm wherein the Wd is the major wavelength of the internal light and the n_intermediate is the refractive index of the intermediate layer 103. In one embodiment, the top width D2 of the cone 102 is smaller than 0.1 nm μm. In order to guide the light to the epitaxial stack 109 through the top 201 before being absorbed within the cone 102, the cone 102 is designed to have an angle θ between the bottom 202 of the cone 102 and the chord 205 of the arc 204 between 40°-60°, preferably to be about 48°.

As described above, with consideration of the light extraction efficiency and the growth rate of the epitaxial layers, a ratio of the top 201 area to the bottom 202 area is designed to be less than 0.0064. Thus the bottom width D1 and the top width D2 of the cone 102 has a relationship represented by a third ratio Q3=(D2/D1) between 0-0.08, preferably between 0-0.03.

According to the light extraction intensity shown in FIG. 2, the height H is expected to be larger to reflect more light. Moreover, the distance S between two adjacent cones 102 and the plane of the top 201 can be C plane suitable for epitaxial growth. Thus the height H, the distance S between two adjacent cones 102 and bottom width D1 form a relationship represented by a fourth ratio Q4=H/(D1+S). In one embodiment, the fourth ratio Q4 is between 0.4-0.6, and in a preferred embodiment, the fourth ratio Q4 is designed to be 0.5 for giving consideration to the growth rate of the epitaxial layers and the light extraction efficiency.

As shown in FIG. 5A, LEDs are designed with two different cone sizes designated as spec I and spec III. The LED of spec III has a patterned substrate with cone size having a first ratio Q1 of 0.13, and the LED of spec I has a patterned substrate of cone size having a first ratio Q1 of 0.25. FIGS. 4A and 4B show the measurement result, wherein the light extraction intensity indicated in FIG. 4A is increased about 20% for the LED of spec III comparing with that of the LED of spec I. As the output power measurement result shown in FIG. 4B and the average value listed in FIG. 5B, the LEDs of spec III have output power 3% larger than what LEDs of spec I have. Both of the two measurement results show the LED of spec III has better light extraction performance than that of the LED with spec I. To sum up, the LEDs of spec III having a first ratio Q1 of 0.13 which is between 0.03-0.15 have better light extraction efficiency than that of the LEDs of spec I having a first ratio Q1 of 0.25 which is between 0.01-0.3. In addition, the measurement results are classified by four tools in order to prove the differences of light characteristics of LEDs are irrelevant to the differences of facilities.

Furthermore, the quality of the epitaxial layers of the LEDs is verified by the factor of WHM (full width at half maximum) tested by XRD (X-ray diffraction) analysis. As shown in FIG. 5B, the LED of spec III has smaller XRD WHM value than that of the LED of spec I, which indicates the LED of spec III has better epitaxial quality. In sum, the LED of spec III not only has better lighting characteristics but also better epitaxial layer quality comparing with the LEDs of spec I.

It should be noted that the proposed various embodiments are not for the purpose to limit the scope of the disclosure. Any possible modifications without departing from the spirit of the disclosure may be made and should be covered by the disclosure.

Claims

1. A light-emitting device, comprising:

a patterned substrate having a plurality of cones, wherein each of the plurality of cones comprises a top having a top width, a bottom having a bottom width, a sidewall between the top and the bottom, and a height h, wherein an area ratio of the top and to the bottom of the cone is less than 0.0064, and H>1.5 μm and the top width is larger than zero; and a light-emitting stack formed on the cones, wherein the light-emitting stack comprises a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer.

2. The light-emitting device according to claim 1, wherein the sidewall between the top and the bottom is inclined.

3. The light-emitting device according to claim 1, wherein the a shape of the top comprises a circle.

4. The light-emitting device according to claim 1, wherein the a shape of the bottom comprises a circle.

5. The light-emitting device according to claim 2, wherein a cross-section of the inclined sidewall comprises an arc with a chord protruded outward.

6. The light-emitting device according to claim 1, further comprising an intermediate layer having a refractive index formed on the patterned substrate.

7. The light-emitting device according to claim 6, wherein the top width is smaller than the a quotient of the a wavelength of light emitted from the light-emitting device divided by the refractive index of the intermediate layer.

8. The light-emitting device according to claim 1, wherein the top width of the cone is smaller than 0.1 μm.

9. The light-emitting device according to claim 5, further comprising a distance between two of the adjacent cones, wherein the distance is between 0.1-0.4 μm.

10. The light-emitting device according to claim 2, wherein an angle between the bottom of the cone and the chord of the arc is between 40-60 degrees.

11. The light-emitting device according to claim 9, wherein a maximum distance between the arc and the chord of the arc is smaller than 0.5 μm.

12. The light-emitting device according to claim 1, wherein a first ratio of the top width of the cone to the bottom width of the cone is smaller than 0.08.

13. The light-emitting device according to claim 1, wherein at least one of the cones satisfies 0.4<h/(D1+S)<=0.6, wherein D1 represents the bottom width of the cone, and S represents the distance between two of the adjacent cones.

14. The light-emitting device according to claim 9, wherein at least one of the cones satisfies 0.01<S/(D1+S)<0.3, wherein D1 represents the top width of the cone, and S represents the distance between two of the adjacent cones.

15. The light-emitting device according to claim 11, wherein at least one of the cones satisfies 0<B/(D I D1+S)<=0.2, wherein D1 represents the top bottom width of the cone, B represents the maximum distance of the arc and the chord of the arc, and S represents the distance between two of the adjacent cones.

16. The light-emitting device according to claim 1, wherein the area of the top of the cone is zero.

17. The light-emitting device according to claim 1, wherein each of the plurality of cones is disposed on the patterned substrate in a predetermined period.

18. The light-emitting device according to claim 17, wherein the predetermined period comprises a fixed period, a variable period, or a quasi-period.

19. A light-emitting device, comprising:

a substrate comprising a plurality of cones, wherein each of the plurality of cones comprises a top having a top width, a bottom having a bottom width, a sidewall between the top and the bottom, and a height h, wherein an area ratio of the top to the bottom of the cone is less than 0.0064, and H>1.5 μm; and

wherein a cross-section of the sidewall comprises an arc with a chord protruded outward, and the one of the plurality of cones satisfies 0<B/(D1+S)<=0.2;

wherein D1 represents the bottom width, B represents a maximum distance between the arc and the chord, and S represents a distance between the one of the plurality of cones and another one of the plurality of cones adjacent to the one of the plurality of cones.

20. The light-emitting device according to claim 19, wherein an angle between the bottom and the chord of the arc is between 40-60 degrees.

21. The light-emitting device according to claim 19, wherein the maximum distance between the arc and the chord is smaller than 0.5 μm.

22. The light-emitting device according to claim 19, wherein a ratio of the top width to the bottom width is smaller than 0.08, and the top width is larger than zero.

23. The light-emitting device according to claim 19, wherein the one of the plurality of cones satisfies 0.4<h/(D1+S)<=0.6.

24. The light-emitting device according to claim 19, wherein the one of the plurality of cones satisfies 0.01<S/(D1+S)<0.3.

25. A light-emitting device, comprising:

a patterned substrate having a plurality of cones, wherein each of the plurality of cones comprises a top having a top width, a bottom having a bottom width, a sidewall between the top and the bottom, and a height h, wherein an area ratio of the top to the bottom of the cone is less than 0.0064, and H>1.5 μm; and

an intermediate layer having a refractive index formed on the patterned substrate;

wherein the top width is smaller than a quotient of a wavelength of light emitted from the light-emitting device divided by the refractive index of the intermediate layer, and the top width is larger than zero.

26. The light-emitting device according to claim 25, wherein a cross-section of the sidewall comprises an arc with a chord protruded outward, and an angle between the bottom and the chord of the arc is between 40-60 degrees.

27. The light-emitting device according to claim 25, wherein a maximum distance between the arc and the chord of the arc is smaller than 0.5 μm.

28. The light-emitting device according to claim 25, wherein a ratio of the top width to the bottom width is smaller than 0.08.

29. The light-emitting device according to claim 25, wherein the one of the plurality of cones satisfies 0.4<h/(D1+S)<=0.6, wherein D1 represents the bottom width, and S represents a distance between the one of the plurality of cones and another one of the plurality of cones adjacent to the one of the plurality of cones.

30. The light-emitting device according to claim 25, wherein the one of the plurality of cones satisfies 0.01<S/(D1+S)<0.3, wherein D1 represents the bottom width, and S represents a distance between the one of the plurality of cones and another one of the plurality of cones adjacent to the one of the plurality of cones.

31. The light-emitting device according to claim 30, wherein 0.03<S/(D1+S)<0.15.

32. The light-emitting device according to claim 25, wherein an area ratio of the top to the bottom is less than 0.0064.