Deep ultraviolet light emitting devices and methods of fabricating deep ultraviolet light emitting devices

• US 8,772,757 B2
• Filed: 02/13/2008
• Issued: 07/08/2014
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Emerson, David Todd, Bergmann, Michael John, Abare, Amber, Haberern, Kevin
• Primary Examiner(s): Sefer, A.
• Application Number:
  US12/030,539
• Publication Number:
  US 20080142783A1
• Time in Patent Office: 2,337 Days
• Field of Search: 257 13- 14, 257/103, 257/190, 257/627
• US Class Current: 257/13
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/12 with a stress relaxation structure, e.g. buffer layer
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 360 nm with wall plug efficiencies of at least than 4% are provided. Wall plug efficiencies may be at least 5% or at least 6%. Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 345 nm with wall plug efficiencies of at least than 2% are also provided. Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 330 nm with wall plug efficiencies of at least than 0.4% are provided. Light emitting devices and methods of fabricating light emitting devices having a peak output wavelength of not greater than 360 nm and an output power of at least 5 mW, having a peak output wavelength of 345 nm or less and an output power of at least 3 mW and/or a peak output wavelength of 330 nm or less and an output power of at least 0.3 mW at a current density of less than about 0.35 μA/μm² are also provided. The semiconductor light emitting devices may have a direct current lifetime of at least 100 hours, at least 500 hours or at least 1000 hours.

Claims

1. A light emitting device, comprising:

a low defect density base structure comprising;

a substrate;

a GaN-based buffer layer having a first smooth surface that is directly on the substrate and a second smooth surface that is remote from the substrate;

a dielectric layer on the second smooth surface that is remote from the substrate; and

a GaN layer on the dielectric layer remote from the GaN-based buffer layer;

a quantum well active region on the low defect density base structure that emits light, the quantum well active region comprising;

a first barrier layer comprising AlGaN;

a first well layer comprising GaN directly on the first barrier layer;

a second barrier layer comprising AlGaN directly on the first well layer;

a second well layer comprising GaN directly on the second barrier layer; and

a third barrier layer comprising AlGaN directly on the second well layer;

an AlGaN layer on the quantum well active region; and

a GaN based contact layer on the AlGaN layer.

2. The light emitting device of claim 1 having a wall plug efficiency of at least 4%.

3. The light emitting device of claim 2, wherein the wall plug efficiency is at least 5%.

4. The light emitting device of claim 2, wherein the wall plug efficiency is at least 6%.

5. The light emitting device of claim 2, wherein the light emitting device has a direct current lifetime of at least 100 hours.

6. The light emitting device of claim 2, wherein the light emitting device has a direct current lifetime of at least 500 hours.

7. The light emitting device of claim 2, wherein the light emitting device has a direct current lifetime of at least 1000 hours.

8. The light emitting device of claim 2, wherein the wall plug efficiency is provided at a current density of less than about 0.35 μ

A/μ

m².

9. The light emitting device of claim 1, wherein the AlGaN layer on the quantum well active region comprises an AlGaN layer doped with a p-type dopant on the quantum well active region and the GaN based contact layer on the AlGaN layer comprises a GaN based contact layer doped with a p-type dopant.

10. The light emitting device of claim 9, wherein the p-type dopant comprises Mg.

11. The light emitting device of claim 1, wherein the first and second barrier layers are doped with Si.

12. The light emitting device of claim 1, wherein the quantum well active region comprises ten quantum well layers and eleven barrier layers with the quantum well layers being disposed between adjacent barrier layers.

13. The light emitting device of claim 1, wherein the light emitting device including the low defect density base structure, the quantum well active region, the AlGaN layer and the GaN based contact layer has an overall thickness of less than about 2.5 μ

m.

14. The light emitting device of claim 1 wherein the substrate comprises SiC.

15. The light emitting device of claim 1 wherein the dielectric layer comprises a discontinuous dielectric layer.

16. The light emitting device of claim 1

wherein the dielectric layer comprises a plurality of mask regions.

17. The light emitting device of claim 16 wherein the mask regions comprise SiN.

18. The light emitting device of claim 1 wherein the GaN layer on the dielectric layer is less than about 2 μ

m thick.

19. The light emitting device of claim 1 wherein the well layer comprises AlGaN and wherein the first and second barrier layers comprise AlGaN having a different concentration of Al than the well layer.

20. The light emitting device of claim 1 wherein the quantum well active region is configured to emit ultraviolet light.

21. The light emitting device of claim 1 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 360 nm.

22. The light emitting device of claim 1 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 345 nm.

23. The light emitting device of claim 1 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 330 nm.

24. The light emitting device of claim 1 wherein the GaN layer on the dielectric layer is doped with n-type dopants.

25. The light emitting device of claim 24, wherein the GaN layer doped with n-type dopants comprises a doped GaN layer having a defect density of less than about 4×

10⁸ cm<sup>−

2</sup>.

26. The light emitting device of claim 24, wherein the GaN layer doped with n-type dopants comprises GaN doped with silicon.

27. The light emitting device of claim 24 wherein the GaN layer on the dielectric layer is less than about 2 μ

m thick.

28. A method of fabricating a light emitting device, comprising:

forming a low defect density base structure comprising;

a substrate;

a GaN-based buffer layer having a first smooth surface that is directly on the substrate and a second smooth surface that is remote from the substrate;

a dielectric layer on the second smooth surface that is remote from the substrate; and

a GaN layer on the dielectric layer remote from the GaN-based buffer layer;

forming a quantum well active region on the low defect density base structure that emits light, the quantum well active region comprising;

a first barrier layer comprising AlGaN;

a first well layer comprising GaN directly on the first barrier layer;

a second barrier layer comprising AlGaN directly on the first well layer;

a second well layer comprising GaN directly on the second barrier layer; and

a third barrier layer comprising AlGaN directly on the second well layer;

forming an AlGaN layer on the quantum well active region; and

forming a GaN based contact layer on the AlGaN layer.

29. The method of claim 28 wherein the light emitting device has a wall plug efficiency of at least 4%.

30. The method of claim 28 wherein the light emitting device has a direct current lifetime of at least 100 hours.

31. The method of claim 28 wherein the light emitting device has an output power of at least 3 mW at a current density of about 0.35 μ

A/μ

m².

32. The method of claim 28 wherein the dielectric layer comprises a discontinuous dielectric layer.

33. The method of claim 28 wherein the dielectric layer comprises a plurality of mask regions.

34. The method of claim 33 wherein the mask regions comprise SiN.

35. The method of claim 28 wherein the GaN layer on the dielectric layer is less than about 2 μ

m thick.

36. The method of claim 28 wherein the well layer comprises AlGaN and wherein the first and second barrier layers comprise AlGaN having a different concentration of Al than the well layer.

37. The method of claim 28 wherein the quantum well active region is configured to emit ultraviolet light.

38. The method of claim 28 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 360 nm.

39. The method of claim 28 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 345 nm.

40. The method of claim 28 wherein the quantum well active region is configured to emit light at a peak output wavelength of not greater than 330 nm.

41. The method of claim 28 wherein the GaN layer on the dielectric layer is doped with n-type dopants.

42. The method of claim 41 wherein the GaN layer on the dielectric layer is less than about 2 μ

m thick.