P-SIDE LAYERS FOR SHORT WAVELENGTH LIGHT EMITTERS

• US 20140231745A1
• Filed: 09/14/2012
• Published: 08/21/2014
• 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
• Granted Patent: US 9,401,452 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 21/0237 Materials
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/02507 Alternating layers, e.g. superlattice
• CPC Class Codes: H01L 21/0251 Graded layers
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 33/007 comprising nitride 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 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01S 5/0421 characterised by the semiconducting contacting layers electrodes H01S5/0425
• CPC Class Codes: H01S 5/0422 with n- and p-contacts on the same side of the active layer
• CPC Class Codes: H01S 5/04257 having positive and negative electrodes on the same side of the substrate
• CPC Class Codes: H01S 5/2009 by using electron barrier layers
• CPC Class Codes: H01S 5/3063 using Mg
• CPC Class Codes: H01S 5/320225 polar orientation
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/3216 : quantum well or superlattice cladding layers
• CPC Class Codes: H01S 5/3404 : influencing the polarisation
• CPC Class Codes: H01S 5/34333 : with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser

Abstract

A light emitting device includes a p-side heterostructure having a short period superlattice (SPSL) formed of alternating layers of Al_xhighGa_1-xhighN doped with a p-type dopant and Al_xlowGa_1-xlowN doped with the p-type dopant, where x_low≦x_high≦0.9. Each layer of the SPSL has a thickness of less than or equal to about six bi-layers of AlGaN.

Claims

1. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) including alternating layers of Al_xhighGa_1-xhighN doped with a p-type dopant and Al_xlowGa_1-xlowN doped with the p-type dopant, where x_low≦

x_high≦

0.9 and each layer of the SPSL has a thickness of less than or equal to about six bi-layers of AlGaN;

an n-side heterostructure; and

an active region configured to emit light disposed between the SPSL and the n-side hetero structure.

2. The device of claim 1, wherein each Al_xhighGa_1-xhighN layer has a thickness, T_high, and each Al_xlowGa_1-xlowN layer has a thickness T_low, wherein T_high and T_low are in a range of about 0.7 nm to about 1.3 nm.

3. The device of claim 1, wherein the SPSL has a total thickness of greater that about 200 nm and less than about 450 nm.

4. The device of claim 1, wherein x_high−

x_low is greater than or equal to about 0.25.

5. The device of claim 1, wherein an average Al composition in the SPSL is about 0.60.

6. The device of claim 1, wherein x_low is about 0.44 and x_high is about 0.75.

7. The device of claim 1, wherein resistivity of the SPSL changes by less than about 50 Ω

-cm over a temperature range of about 400 K to about 100 K.

8. The device of claim 1, wherein resistivity of the SPSL is less than about 10 Ω

-cm at room temperature.

9. The device of claim 1, wherein the n-side heterostructure, active region, and p-side heterostructure are grown on at least one of a substrate comprising one or more of GaN, AlN, SiC, sapphire, Si, GaAs, ZnO, a group III-N alloy, and a template comprising a group III-N material.

10. The device of claim 1, wherein the n-side heterostructure, active region, and p-side heterostructure are epitaxially grown on a bulk AlN substrate.

11. The device of claim 1, further comprising a substrate of sapphire, a group-III nitride, SiC, or ZnO, wherein the n-side heterostructure, active region, and p-side heterostructure are epitaxially grown on an (0001) or (000 1) surface of the substrate.

12. The device of claim 1, further comprising a substrate of a group-III nitride, SiC, or ZnO, wherein the n-side heterostructure, active region and p-side heterostructure are epitaxially grown on a semi-polar facet of the substrate.

13. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) comprising alternating layers of Al_xhighGa_1-highN doped with a p-type dopant and Al_xlowGa_1-xlowN doped with the p-type dopant, where x_low≦

x_high<

0.9;

an n-side heterostructure; and

an active region configured to emit light disposed between the SPSL and the n-side heterostructure, wherein the alternating layers cause modulation in a valence band potential in the SPSL and the modulation is approximately equal to an acceptor level energy of the p-type dopant.

14. The device of claim 13, wherein the p-type dopant is Mg and the modulation is greater than about 0.35 eV.

15. A light emitting device, comprising:

a p-side heterostructure;

an n-side heterostructure;

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

a metallic p-contact; and

a p-contact layer disposed between the p-side heterostructure and the p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z has an S-shaped Al composition profile that varies over a substantial portion of the thickness of the p-contact layer.

16. The device of claim 15, wherein:

d is distance in the p-contact layer, wherein d=0 at an interface between the p-side heterostructure and the p-contact layer, and d=D at an interface between the p-contact layer and the p-contact, and d_W is a point between d=0 and d=D; and

the S-shaped profile comprises;

a first portion in which z is concave downward between the d=0 and d=d_W; and

a second portion in which z is concave upward from d=d_W to d=D.

17. The device of claim 16, wherein d_W is greater than about 30% of the thickness of the p-contact layer.

18. The device of claim 17, wherein D is about 100 nm.

19. The device of claim 15, wherein z decreases from about 0.7 proximate to the p-side heterostructure to about 0 proximate to the p-contact.

20. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) comprising alternating layers of Al_xhighGa_1-xhighN doped with a p-type dopant and Al_xlowGa_1-xlowN doped with the p-type dopant, where x_low≦

x_high≦

0.9;

an n-side heterostructure;

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

a metallic p-contact; and

a p-contact layer disposed between the p-side heterostructure and the p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z varies over a substantial portion of the thickness of the p-contact layer.

21. The device of claim 20, wherein x_low≦

x_high≦

0.9 and a thickness of each of the alternating layers is less than or equal to about six AlGaN bi-layers.

22. The device of claim 20, wherein:

z decreases linearly with slope g₁ in a first region extending from d=0 at an interface between the p-side heterostructure and the p-contact layer to d=d_mid; and

z decreases linearly with slope g₂ in a second region extending from d=d_mid to d=D at an interface between the p-contact layer and the p-contact, wherein a magnitude of g₂ is greater than a magnitude of g₁.

23. The device of claim 22, wherein a thickness of the SPSL is less than about 260 nm and d_mid is greater than about 60 nm.

24. The device of claim 20, wherein:

d is distance in the p-contact layer;

d=0 at an interface between the p-side heterostructure and the p-contact layer;

d=D at an interface between the p-contact layer and the p-contact;

d_W is a point between d=0 and d=D; and

the p-contact layer includes;

a first portion in which z is concave downward between d=0 and d=d_W; and

a second portion in which z is concave upward from d=d_W to d=D.

25. The device of claim 24, wherein the thickness of the SPSL is less than about 260 nm and d_W is greater than about 60 nm.

26. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL);

an n-side heterostructure; and

an active region configured to emit light disposed between the SPSL and the n-side heterostructure, wherein the SPSL comprises a first portion and a second portion, the first portion proximate the active region and comprising a first number of alternating layers of Al_x1highGa_1-x1highN doped with a p-type dopant and Al_x1lowGa_1-x1lowN doped with the p-type dopant, the second portion comprising a second number of alternating layers of Al_x2highGa_1-x2highN doped with a p-type dopant and Al_x2lowGa_1-x2lowN doped with a p-type dopant, and wherein a thickness of each layer of the SPSL has a thickness of less than or equal to about six bi-layers of AlGaN.

27. The device of claim 26, wherein x_2low≦

x_2high≦

0.9.

28. The device of claim 26, wherein an Al composition and thickness of the Al_x1highGa_1-x1highN and Al_x1lowGa_1-x1lowN layers are configured to provide significant retention of electrons in the active region.

29. The device of claim 26, wherein at least some layers of the first portion have a thickness greater than a thickness of the layers of the second portion.

30. The device of claim 26, wherein the first number is about 6.

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

growing an n-side heterostructure on a substrate;

growing an active region on the n-side heterostructure;

growing a short period superlattice (SPSL) proximate to the active region, comprising;

growing alternating layers of Al_xhighGa_1-xhighN doped with a p-type dopant and Al_xlowGa_1-xlowN doped with the p-type dopant, where x_low≦

x_high≦

0.9 and each layer of the SPSL having a thickness of less than or equal to about six bi-layers of AlGaN.

32. The method of claim 31, wherein growing the alternating layers comprises growing the alternating layers using metalorganic chemical vapor deposition (MOCVD) at an ambient pressure of in a range of about 80 to about 700 torr.

33. The method of claim 31, wherein growing the alternating layers comprises growing the alternating layers at a temperature between about 750°

C. and 1300°

C.

34. The method of claim 31, wherein growing the alternating layers comprises growing the alternating layers at a growth rate between about 0.01 nm per second to 0.04 nm per second.