ULTRAVIOLET LIGHT EMITTING DEVICES HAVING ENHANCED LIGHT EXTRACTION

• US 20130082237A1
• Filed: 12/16/2011
• Published: 04/04/2013
• Est. Priority Date: 10/04/2011
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Northrup, John E., Chua, Christopher L., Kneissl, Michael, Wunderer, Thomas, Johnson, Noble M.
• Granted Patent: US 9,252,329 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: H01L 33/0025 comprising only AIIIBV compounds
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: H01L 33/04 with a quantum effect structure or superlattice, e.g. tunnel junction
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

Light emitting devices having an enhanced degree of polarization, P_D, and methods for fabricating such devices are described. A light emitting device may include a light emitting region that is configured to emit light having a central wavelength, λ, and a degree of polarization, P_D, where P_D>0.006λ−b for 200 nm≦λ≦400 nm, wherein b≦1.5.

Claims

1. A nitride-semiconductor light emitting device comprising a light emitting region configured to emit light having a central wavelength, λ

, and a degree of polarization, P_D, where P_D>

0.006λ

−

b for 200 nm≦

λ

≦

400 nm, wherein b≦

1.5.

2. The device of claim 1, wherein b is about 1.

3. The device of claim 1, wherein the light emitting region comprises at least one of GaN, InAlN, AlGaN, InGaN and InAlGaN.

4. The device of claim 1, further comprising a substrate, the substrate comprising at least one of sapphire, GaN, AlN, AlGaN, InAlGaN, Si, and SiC.

5. The device of claim 1, further comprising a bulk crystalline AlN substrate.

6. The device of claim 5, wherein:

the AlN substrate has a lattice constant, a_bulk-AlN;

the light emitting region comprises at least one Al_xGa_1-xN region; and

the at least one Al_xGa_1-xN region has an in-plane lattice constant a_strained and a_strained−

a_bulk-AlN≦

(λ

(nm)−

230)*0.0012 Å

.

7. The device of claim 6, wherein the Al_xGa_1-xN region is disposed between two Al_yGa_1-yN regions, where y>

x and y>

0.7+0.02*(245−

λ

(nm)).

8. The device of claim 1, wherein the light emitting region comprises at least one Al_xGa_1-xN layer and wherein the strain ε

_a in the Al_xGa_1-xN layer satisfies the inequality ε

_a<

−

0.0079+0.00022*(λ

(nm)−

240 nm).

9. The device of claim 1, wherein λ

≦

300 nm and P_D≧

0.

10. The device of claim 1, wherein the light emitting region is disposed between first and second heterostructures, wherein the first heterostructure is disposed between the light emitting region and the substrate and comprises at least one of:

an AlGaN/AlGaN short period superlattice; and

an AlGaN layer having a first surface near the substrate and a second surface near the light emitting region, the AlGaN layer graded in Al content between the first surface and the second surface.

11. The device of claim 10, further comprising a base layer disposed between the substrate and the first heterostructure, wherein the base layer comprises Al_zbaseGa_1-zbaseN, where zbase is between 0 and 1.

12. The device of claim 10, wherein the first heterostructure comprises a transition layer comprising a two section short period AlN/GAN superlattice.

13. The device of claim 12, wherein:

a first section of the transition layer has an average aluminum molar fraction of about 90%; and

a second section of the transition layer has an average aluminum, molar fraction of about 80%.

14. The device of claim 12, wherein a transition layer surface closest to the light emitting region has a surface roughness less than about 10 nm.

15. A light emitting device, comprising a light emitting region grown above a bulk crystalline AlN substrate, wherein variation in reciprocal lattice values of the AlN substrate and the light emitting region is less than about 1.5%.

16. The device of claim 15, wherein the light emitting region is configured to emit light having a central wavelength, λ

, and a degree of polarization, P_D, where P_D is greater than P_D is greater than 0.006 λ

−

1.5 for 200≦

λ

≦

400 nm.

17. The device of claim 15, wherein:

the AlN substrate has a lattice constant, a_bulk-AlN;

the light emitting region comprises at least one Al_xGa_1-xN region; and

the at least one Al_xGa_1-xN region has an in-plane lattice constant a_strained t satisfies the inequality a_strained−

a_bulk-AlN≦

(λ

(nm)−

230)*0.0012 Å

.

18. The device of claim 17, wherein the Al_xGa_1-xN region is disposed between two Al_yGa_1-yN regions, and wherein y>

x and y>

0.7+0.02*(245−

λ

(nm)).

19. A light emitting device comprising a light emitting region configured to emit light having a central wavelength, λ

, and a degree of polarization, P_D, where P_D>

0 for 200 nm≦

λ

<

300 nm.

20. The device of claim 19, further comprising an AlN substrate, wherein the light emitting region is grown over the AlN substrate.

21. The device of claim 19, wherein:

the AlN substrate has a lattice constant, a_bulk-AlN;

the light emitting region comprises at least one Al_xGa_1-xN region; and

the at least one Al_xGa_1-xN region has an in-plane lattice constant a_strained and a_strained−

a_bulk-AlN≦

(λ

(nm)−

230)*0.0012 Å

.

22. A method of forming a light emitting device, comprising:

growing a first heterostructure;

growing a second heterostructure; and

growing a III-nitride light emitting region over the first heterostructure so that the light emitting region is disposed between the first heterostructure and the second heterostructure, the light emitting region comprising at least one compressively stained layer, wherein a compressive strain, ε

_a, in the compressively strained layer satisfies the inequality ε

_a<

−

0.00615+0.00023*(λ

(nm)−

230 nm).

23. The method of claim 22, wherein growing the first heterostructure comprises growing the first heterostructure on a GaN, AlN, AlGaN, InAlGaN, Si, or SiC substrate.

24. The method of claim 22, wherein the light emitting device is capable of emitting light having a central wavelength, λ

, a degree of polarization P_D≧

0 for 200≦

λ

≦

300.

25. The method of claim 22, wherein the light emitting region is capable of emitting light having a central wavelength, λ

, and a degree of polarization, P_D>

0.006 λ

−

1.5 for 200 nm≦

λ

≦

400 nm.

26. The method of claim 22, wherein:

growing the first heterostructure comprises growing the first heterostructure above an AlN substrate; and

growing the III-nitride light emitting region comprises growing the light emitting region so that a variation in reciprocal lattice values of the AlN substrate and the light emitting region is less than about 1.5%.

27. The method of claim 22, wherein:

growing the first heterostructure comprises growing the first heterostructure above an AlN substrate having a lattice constant a_bulk-AlN;

the at least one compressively strained layer has a lattice constant, a_strained, where a_strained−

a_bulk-AlN≦

(λ

(nm)−

230)*0.0012 Å

.

28. The method of claim 27, further comprising:

homoepitaxially growing an AlN layer above the AlN substrate so that the homoepitaxially grown AlN layer is disposed between the first heterostructure and the AlN substrate; and

removing some or all of the AlN substrate.

29. The method of claim 28, further comprising removing at least some of the homoepitaxially grown AlN layer.

30. The method of claim 27, further comprising:

epitaxially growing an AlGaN or AlGaInN layer above the AlN substrate so that the epitaxially grown AlGaN or AlGaInN layer is disposed between the first heterostructure and the AlN substrate; and

removing some or all of the AlN substrate.

31. The method of claim 30, further comprising removing at least some of the epitaxially grown AlGaN or AlGaInN layer.

32. The method of claim 22, wherein growing the first heterostructure comprises growing a transition layer comprising a two section AlN/GAN superlattice.

33. The method of claim 22, wherein growing III-nitride light emitting region comprises:

growing barrier layers comprising Al_yGa_1-yN; and

growing quantum wells comprising Al_xGa_1-xN disposed between the barrier layers, wherein y>

x and y>

0.7+0.02*(245−

λ

(nm)).

34. A light emitting device comprising at least one compressively stained layer of Al_xGa_1-xN, wherein 0.5<

x<

0.8, and wherein a compressive strain, ε

_a, in the compressively strained layer satisfies the inequality ε

_a<

−

0.00615.