Graded electron blocking layer

• US 9,219,189 B2
• Filed: 09/14/2012
• Issued: 12/22/2015
• Est. Priority Date: 09/14/2012
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Northrup, John E., Cheng, Bowen, Chua, Christopher L., Wunderer, Thomas, Johnson, Noble M., Yang, Zhihong, Choi, Suk
• Primary Examiner(s): Niesz, Jamie C
• Application Number:
  US13/619,687
• Publication Number:
  US 20150280056A1
• Time in Patent Office: 1,194 Days
• Field of Search: 257/13, 257/14, 257/94, 257/97, 257/E33.049, 257/E33.008, 257/101, 438/47
• US Class Current: 1/1
• CPC Class Codes: H01L 33/0025 comprising only AIIIBV compounds
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/145 with a current-blocking structure
• CPC Class Codes: H01L 33/16 with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous

Abstract

A light emitting device includes a p-side heterostructure, an n-side heterostructure, an active region disposed between the p-side heterostructure and the n-side heterostructure. An electron blocking layer (EBL) disposed between the p-side heterostructure and the active region comprises an aluminum containing group-III-nitride alloy. An aluminum composition of the EBL decreases as a function of distance along a [0001] direction from the active region towards the p-side heterostructure over a majority of the thickness of the EBL.

Claims

1. A light emitting device, comprising:

a p-side heterostructure;

an n-side heterostructure;

an active region disposed between the p-side heterostructure and the n-side heterostructure and configured to emit light;

an electron blocking layer (EBL) disposed on a growth surface and arranged between the p-side heterostructure and the active region, the EBL having a thickness and comprising an aluminum containing group-III-nitride alloy; and

a p-side superlattice disposed on the electron blocking layer,

wherein an aluminum composition of the EBL changes as a function of distance along a growth direction-from the active region towards the p-side heterostructure over a majority of the thickness of the EBL, and wherein the change in the aluminum composition is dependent on growth surface orientation, wherein the aluminum composition in the EBL decreases along the growth direction for a growth surface orientation having crystallographic indices (hk( h+k)m) with m greater than zero or the aluminum composition in the EBL increases along the growth direction for a growth surface orientation having crystallographic indices (hk( h+k)m) with m less than zero.

2. The device of claim 1, wherein the aluminum containing group-III-nitride alloy comprises InAlN.

3. The device of claim 1, wherein the aluminum containing group-III-nitride alloy comprises AlGaN.

4. The device of claim 1, wherein the EBL is configured so that a conduction band energy of the EBL decreases as a function of distance along a direction from the active region towards the p-side heterostructure over a majority of the thickness of the EBL.

5. The device of claim 1, wherein the EBL is configured so that a polarization within the EBL increases as a function of distance along a direction from the active region towards the p-side heterostructure over a majority of the thickness of the EBL.

6. The device of claim 1, wherein the active region is configured to emit light in a wavelength range of about 200 nm to about 365 nm.

7. The device of claim 1, wherein the active region is configured to emit light in a wavelength range of about 365 nm to about 550 nm.

8. The device of claim 1, wherein the active region is configured to emit light in a wavelength range greater than about 550 nm to about 700 nm.

9. A light emitting device, comprising:

a p-side heterostructure;

an n-side heterostructure;

an active region disposed between the p-side heterostructure and the n-side heterostructure and configured to emit light; and

an electron blocking layer (EBL) disposed between the p-side heterostructure and the active region and having a thickness, the EBL comprising Al_yGa_1-yN, wherein y is graded in a number of discrete steps, a width of the steps changing as a function of distance along a growth direction from the active region towards the p-side heterostructure over a majority of the thickness of the EBL, wherein an aluminum composition of the EBL changes as a function of distance along the growth direction-from the active region towards the p-side heterostructure over a majority of the thickness of the EBL, wherein the change in the aluminum composition is dependent on growth surface orientation, wherein the aluminum composition in the EBL decreases along the growth direction for a growth surface orientation having crystallographic indices (hk( h+k)m) with m greater than zero or the aluminum composition in the EBL increases along the growth direction for a growth surface orientation having crystallographic indices (hk( h+k)m) with m less than zero.

10. The device of claim 9, further comprising an AlN substrate wherein the n-side heterostructure is grown on the (0001) surface of the AlN substrate.

11. The device of claim 9, wherein a difference between a first value y in the EBL proximate the active region and a second value of y in the EBL proximate the p-side heterostructure is about 0.35.

12. The device of claim 9, wherein a first value of y in the EBL proximate the active region is in a range of about 0.8 to about 1 and a second value of y in the EBL proximate the p-side heterostructure is in a range of about 0.5 to 0.7.

13. The device of claim 9, wherein y decreases with distance at a rate of about 30% in 10 nm.

14. The device of claim 9, wherein a first value of y in the EBL proximate the active region is in a range of about 0.1 to about 0.3 and a second value of y in the EBL proximate the p-side heterostructure is in a range of about 0 to 0.1, and wherein the active region is configured to emit light in a wavelength range between about 365 nm and 550 nm.

15. The device of claim 9, wherein the EBL is configured so that a conduction band energy of the EBL decreases as a function of distance along a direction from the active region towards the p-side heterostructure, the conduction band energy decreasing from a first conduction band value to a second conduction band value over a majority of the thickness of the EBL.

16. The device of claim 15, wherein the EBL is configured so that:

an electron quasi Fermi level in the EBL is more than about 0.25 eV from the conduction band energy over a majority of the thickness of the EBL; and

a hole quasi Fermi level in the EBL is less than about 0.1 eV from the valence band energy over a majority of the thickness of the EBL.

17. A light emitting device, comprising:

a p-side heterostructure;

an n-side heterostructure;

an active region disposed between the p-side heterostructure and the n-side heterostructure and configured to emit light, the active region comprising a III-nitride material; and

an electron blocking layer (EBL) disposed on a growth surface and arranged between the p-side heterostructure and the active region, the EBL having a thickness and comprising an aluminum containing group III-nitride alloy, wherein a change in an aluminum composition of the EBL is dependent on orientation of a growth surface, and

wherein the growth surface orientation is a semi-polar growth surface orientation identified by crystallographic indices (hk( h+k)m) with m>

0 and the aluminum composition in the EBL decreases as a function of distance along a growth direction normal to the growth surface over a majority of a thickness of the EBL, or

the growth surface orientation is a semi-polar growth surface orientation identified by crystallographic indices (hk( h+k)m) with m<

0 and the aluminum composition increases as a function of distance along the growth direction normal to the growth surface over a majority of a thickness of the EBL.

18. The device of claim 17, wherein m<

0 and the aluminum composition in the EBL increases at a rate of about 30% in 10 nm.

19. The device of claim 17, wherein the EBL comprises Al_yGa_1-yN or In_1-yAl_yN, and y in the EBL proximate the active region is about 0.8 to about 1 and y in the EBL proximate the p-side heterostructure is about 0.5 to about 0.85.

20. The device of claim 17, wherein m>

0 and the aluminum composition decreases at a rate of about 30% in 10 nm.

21. A light emitting device, comprising:

a p-side heterostructure;

an n-side heterostructure;

an active region disposed between the p-side heterostructure and the n-side heterostructure and configured to emit light, the active region comprising a number of quantum wells separated by barriers, the barriers including a last barrier comprising Al_zGa_1-zN, only a portion of the last barrier being doped with a p-type dopant; and

an electron blocking layer (EBL) disposed on a growth surface and arranged between the p-side heterostructure and the last barrier, the EBL comprising Al_yGa_1-yN, wherein y changes as a function of distance from the last barrier and the change in y is dependent on orientation of the growth surface, wherein y decreases as a function of distance along a growth direction over a majority of a thickness of the EBL for a growth surface orientation identified by crystallographic indices (hk( h+k)m) with m>

0 or y increases as a function of distance along the growth direction over a majority of the thickness of the EBL for a growth surface orientation identified by crystallographic indices (hk( h+k)m) with m<

0, and

wherein a value of z proximate the EBL is greater than the value of z proximate the quantum well.

22. The device of claim 21, wherein the EBL is configured so that a conduction band energy of the EBL decreases as a function of distance along a direction from the active region towards the p-side heterostructure, the conduction band energy decreasing from a first conduction band value to a second conduction band value over a majority of the thickness of the EBL.

23. The device of claim 22, wherein the EBL is configured so that:

an electron quasi Fermi level in the EBL is more than about 0.25 eV from the conduction band energy over a majority of the thickness of the EBL; and

a hole quasi Fermi level in the EBL is less than about 0.1 eV from the valence band energy over a majority of the thickness of the EBL.

24. The device of claim 21, wherein a difference between a first value of z in the last barrier proximate a last quantum well and a second value of z in the last barrier proximate the EBL is about 0.25.

25. The device of claim 21, wherein a first value of z in the last barrier proximate a last quantum well is about 0.54 and a second value of z in the last barrier proximate the EBL is about 0.8.

26. The device of claim 21, wherein a thickness of the last barrier is between about 4 nm to about 20 nm.

27. The device of claim 21, wherein z increases in a series of steps over a thickness of the last barrier, each step having a step thickness in a range of about 1 to about 3 nm.

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

growing an n-side heterostructure on a polar or semipolar face of a substrate;

growing an active region comprising one or more quantum wells disposed between barriers, the active region configured to emit light during operation of the light emitting device;

growing a p-side heterostructure; and

growing an electron blocking layer on the active region, wherein the electron blocking layer (EBL) is grown on a growth surface and is disposed between the p-side heterostructure and the active region, the EBL having a thickness and comprising an aluminum containing group III-nitride alloy, wherein;

growing the EBL comprises grading an aluminum composition of the EBL dependent on orientation of the growth surface such that the growth surface orientation has crystallographic indices (hk( h+k)m) with m>

0 and the aluminum composition in the EBL decreases as a function of distance over a majority of the thickness of the EBL along a growth direction normal to the growth surface or the growth surface orientation has crystallographic indices (hk(h+k)m) with m<

0 and the aluminum composition in the EBL increases as a function of distance over a majority of the thickness of the EBL along the growth direction normal to the growth surface.

29. The method of claim 28, wherein

growing the active region comprises growing a last barrier between a last quantum well and the EBL and a first aluminum composition in the last barrier proximate the EBL is greater than a second aluminum composition in the last barrier proximate the last quantum well;

and

only a portion of the last barrier is doped with a p-type dopant, the portion being farthest from the last quantum well.