High-brightness light-emitting diode with surface microstructures
A high-brightness light-emitting diode with surface microstructure and preparation and screening methods thereof are provided. The ratio of total roughened surface area of light transmission surface of a light emitting diode to vertically projected area is greater than 1.5, and the peak density of light transmission surface is not less than 0.3/um 2 . The higher the ratio of total roughened surface area of an epitaxial wafer to vertically projected area and the higher the number of peak over the critical height within a unit area, the more beneficial to improve light extraction efficiency of the epitaxial wafer. As a result, light extraction efficiency of the epitaxial wafer is greatly improved.
1. A method of making a high-brightness light-emitting diode (LED), the method comprising:
(1) exposing a light-emitting surface of an epitaxial wafer of the LED to be roughened, and protecting the light-emitting surface not-to-be roughened with a photoresist or metal;
(2) preparing a roughening solution based on dose proportions in weight percentages as:
CH 3 COOH
30~50%
HF
40~60%
H 2 SO 4
0~2%
HNO 3
0~20%
H3PO4
0~10%
(3) dipping the epitaxial wafer processed by Step (1) in the roughening solution prepared by Step (2) for 1-8 min;
wherein for the resulting LED:
the light-emitting surface has a surface microstructure; and
a ratio of total roughened surface area of the light-emitting surface to a vertically-projected area is not less 1.5.
2. The method of 1 , further comprising: drying the epitaxial wafer for subsequent preparation of the LED.
3. The method of claim 1 , wherein:
the epitaxial wafer processed by Step (1) comprises a high reflection metal surface with electric contact and mirror system; and
a bonding metal is evaporated over the mirror system and achieves bonding effect by applying a high temperature and a high pressure.
4. The method of claim 3 , wherein: the high temperature is 250-350° C., and the high pressure is 60-200 KPa.
5. A method of selecting high-brightness light-emitting diodes (LEDs), the method comprising:
(1) selecting an epitaxial wafer with a surface roughened;
(2) measuring a total roughened surface area of a light-emitting surface on the epitaxial wafer selected in Step (1);
(3) calculating a ratio of the total roughened surface area to a vertically projected area;
(4) selecting epitaxial wafers with the ratio of not less than 1.5; and
(5) fabricating LEDs with the epitaxial wafers selected in Step (4);
wherein for the LEDs:
the light-emitting surface has a surface microstructure; and
a ratio of total roughened surface area of the light-emitting surface to a vertically-projected area is not less 1.5.
6. The method of claim 5 , wherein the fabricating comprises:
(a) exposing a light-emitting surface of an epitaxial wafer of the LED to be roughened, and protecting the light-emitting surface not-to-be roughened with a photoresist or metal;
(b) preparing a roughening solution based on dose proportions in weight percentages as:
CH 3 COOH
30~50%
HF
40~60%
H 2 SO 4
0~2%
HNO 3
0~20%
H3PO4
0~10%
(c) dipping the epitaxial wafer processed by Step (1) in the roughening solution prepared by Step (2) for 1-8 min.
7. The method of claim 6 , wherein the fabricating further comprises: drying the epitaxial wafer for subsequent preparation of the LED.
8. The method of claim 6 , wherein:
the epitaxial wafer processed by Step (a) comprises a high reflection metal surface with electric contact and mirror system; and
a bonding metal is evaporated over the mirror system and achieves bonding effect by applying a high temperature and a high pressure.
9. The method of claim 8 , wherein: the high temperature is 250-350° C., and the high pressure is 60-200 KPa.
10. The method of claim 5 , wherein a peak density of the light-emitting surface is not less than 0.3/um 2 .
11. The method of claim 10 , wherein:
the light-emitting surface is of a layer that is Al doped GaInP layer or Mg doped GaP layer, and
in the Al doped GaInP layer, a mol ratio of Al to GaInP is 0.67-1.5.