Method of making a light emitting diode

• US 7,413,918 B2
• Filed: 01/11/2005
• Issued: 08/19/2008
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: SemiLEDs Corporation (SemiLEDs Inc)
• Original Assignee: SemiLEDs Corporation (SemiLEDs Inc)
• Inventors: Tran, Chuong Anh, Doan, Trung Tri
• Primary Examiner(s): Mulpuri, Savitri
• Application Number:
  US11/032,881
• Publication Number:
  US 20060154392A1
• Time in Patent Office: 1,316 Days
• Field of Search: 438 22- 47
• US Class Current: 438/46
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

Methods are disclosed for forming a vertical semiconductor light emitting diode (VLED) device having an active layer between an n-doped layer and a p-doped layer; and securing a plurality of balls on a surface of the n-doped layer of the VLED device.

Claims

1. A method of fabricating a semiconductor light-emitting diode (LED) device, comprising:

forming a multi-layer epitaxial structure of the LED device that includes;

an n-doped layer;

an active layer adjacent the n-doped layer;

a p-doped layer adjacent the active layer, wherein the n-doped layer is at least about four times thicker than the p-doped layer; and

a metal substrate adjacent the p-doped layer, wherein both the n-doped layer and the p-doped layer include gallium nitride;

providing a plurality of balls on a surface of the n-doped layer of the LED device; and

roughening the surface of the n-doped layer to scatter and extract light from interior for emission out of the n-doped layer;

depositing an optically transparent and electrically conductive contact layer above the plurality of balls, whereby a bias applied across the p-doped layer and the n-doped layer generates light that is emitted through the n-doped layer, scattered by the plurality of balls, and emitted to the ambient via the contact layer.

2. The method as defined in claim 1, further comprising using one of spin coating and spraying the balls on the n-doped layer of the LED device.

3. The method as defined in claim 1, further comprising controlling the density of the balls by adjusting a viscosity of an applied ball-containing solution.

4. The method as defined in claim 1, wherein:

the n-doped layer has a thickness in a range from about 2 microns to about 6 microns; and

the p-doped layer has a thickness in a range from about 0.05 microns to about 0.5 microns.

5. The method as defined in claim 1, further comprising securing the balls on the surface of the n-doped layer of the LED device.

6. The method as defined in claim 1, wherein the balls are planar with the n-doped layer of the LED device.

7. The method as defined in claim 1, wherein the contact layer is greater than 80 percent transparent to the wavelength that the LED transmits.

8. The method as defined in claim 5, wherein the securing the balls comprises applying a clear coat to hold the balls.

9. The method as defined in claim 5, wherein the securing the balls comprises applying a conductive coat to hold the balls.

10. The method as defined in claim 5, wherein the securing the balls comprises applying sol-gel to hold the balls.

11. The method as defined in claim 5, wherein the securing the balls comprises spray coating or spin coating the balls.

12. The method as defined in claim 1, wherein the balls are dispersed in an organic solution.

13. The method as defined in claim 5, wherein the securing the balls comprises applying dry powder coating.

14. The method as defined in claim 13, comprising applying electrostatic coating to hold the balls.

15. The method as defined in claim 1, wherein the contact layer comprises one of indium tin oxide (ITO), Nickel, and Gold.

16. The method as defined in claim 1, wherein one of the balls comprises a sub-micron sphere.

17. The method as defined in claim 1, wherein one of the balls has a radius between approximately 10 nm and about 2 micron.

18. The method as defined in claim 1, wherein the dimension of the balls is selected to optimally scatter light at approximately ½

λ

.

19. The method as defined in claim 1, wherein a refractive index of one of the balls is between approximately 2.0 and 3.0.

20. The method as defined in claim 1, wherein a refractive index of one of the balls is greater than approximately 2.3.

21. The method as defined in claim 1, wherein a refractive index of one of the balls is approximately equal to a refractive index of the n-doped layer.

22. The method as defined in claim 1, wherein one of the balls comprises one of TiO2, Ta2O5, ZrO, ZnO, HfO2, GaN, AlN, ZnSe, and SiOxNy.

23. The method as defined in claim 1, wherein the balls are spread on a surface of the n-doped layer of the LED device using a coating method.

24. The method as defined in claim 5, wherein the secured balls form a mask for dry etching the n-doped layer.

25. The method as defined in claim 24, wherein the etched n-doped layer of the LED device increases LED surface roughness to extract more light from an interior thereof.

26. The method as defined in claim 1, wherein the active layer is a multiple quantum well (MQW) active layer.

27. The method as defined in claim 1, wherein the contact layer comprises indium tin oxide (ITO) deposited using one of physical vapor deposition (PVD), chemical vapor deposition (CVD), and e-beam evaporation.

28. The method as defined in claim 1, wherein the contact layer is deposited using one of physical vapor deposition (PVD), chemical vapor deposition (CVD), and e-beam evaporation.

29. A method comprising:

forming a vertical light-emitting diode (VLED) device having an active layer between an n-doped layer and a p-doped layer, wherein both the n-doped layer and the p-doped layer include gallium nitride and the n-doped layer is at least about four times thicker than the p-doped layer;

forming a conductive substrate such that the p-doped layer is between the active layer and the conductive substrate;

securing a plurality of balls for light extraction on a surface of the n-doped layer of the VLED device by forming an optically transparent and electrically conductive contact layer above the plurality of balls, whereby biasing the p-doped layer and n-doped layer causes the emission of light substantially through the n-doped layer to the ambient via the contact layer; and

roughening the surface of the n-doped layer.

30. The method as defined in claim 29, wherein the securing is selected from the group consisting of:

spinning a coating over the balls;

spraying a coating over the balls;

applying a coating over the balls that is greater than 80 percent transparent to the wavelength that the VLED transmits;

applying a conductive coat over the balls;

applying sol-gel over the balls;

applying a dry powder coating over the balls;

applying an electrostatic coating over the balls;

applying a coating over the balls comprising one of indium tin oxide (ITO), Nickel, and Gold; and

applying a transparent coating using one of physical vapor deposition (PVD), chemical vapor deposition (CVD), and e-beam evaporation.

31. The method as defined in claim 29, further comprising, prior to said securing, roughening the surface of the n-doped layer of the VLED device.

32. The method as defined in claim 31, further comprising dry etching the n-doped layer using the secured balls as a mask.

33. The method as defined in claim 29, wherein each of the balls comprises a sub-micron sphere having a refractive index approximately equal to that of the n-doped layer.

34. The method as defined in claim 29, wherein one of the balls comprises one of TiO2, Ta2O5, ZrO, ZnO, HfO2, GaN, AlN, ZnSe, and SiOxNy.

35. The method as defined in claim 29, wherein:

the n-doped layer has a thickness in a range from about 2 microns to about 6 microns; and

the p-doped layer has a thickness in a range from about 0.05 microns to about 0.5 microns.

36. A method comprising:

forming, for a vertical light-emitting diode (VLED) device, a multiple quantum well (MQW) active layer between an n-doped layer and a p-doped layer, wherein both the n-doped layer and the p-doped layer include gallium nitride and the n-doped layer is at least about four times thicker than the p-doped layer;

forming a conductive substrate such that the p-doped layer is between the active layer and the conductive substrate;

securing a plurality of balls for light extraction to the n-doped layer;

roughening the surface of the n-doped layer;

depositing an optically transparent and electrically conductive contact layer above the plurality of balls; and

forming opposing electrodes in electrical communication, respectively, with the n-doped layer and the p-doped layer, whereby a bias applied across the p-doped layer and the n-doped layer causes holes and electrons to be injected into the active layer so as to recombine and generate light that is emitted to the ambient via the contact layer after passing through the n-doped layer and being scattered by the plurality of balls.

37. The method as defined in claim 36, wherein:

the n-doped layer has a thickness in a range from about 2 microns to about 6 microns; and

the p-doped layer has a thickness in a range from about 0.05 microns to about 0.5 microns.