P-side layers for short wavelength light emitters

• US 9,401,452 B2
• Filed: 09/14/2012
• Issued: 07/26/2016
• 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
• Primary Examiner(s): Parendo, Kevin
• Application Number:
  US13/619,598
• Publication Number:
  US 20140231745A1
• Time in Patent Office: 1,411 Days
• Field of Search: 257/103
• US Class Current: 1/1
• 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 six bi-layers of AlGaN, each bi-layer being one layer of Al and Ga atoms and one layer of N atoms and having a thickness of 0.25 nm;

an n-side heterostructure; and

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

a difference between x_low and xhigh in the alternating layers causes modulation of a valance band edge energy in the SPSL, and

the modulation of the valence band edge energy in the SPSL is at least an acceptor energy level of the p-type dopant.

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 0.7 nm to 1.3 nm.

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

4. The device of claim 1, wherein x_high−

x_low is greater than or equal to 0.25.

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

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

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

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

8. The device of claim 1, wherein a resistivity of the SPSL is less than 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 (0001) 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. The device of claim 1, wherein the modulation of the valence band energy edge is equal to a sum of a valence band offset between the alternating layers in the SPSL and a change in potential within a layer of the SPSL arising from polarization charges at interfaces of the alternating layers.

14. The device of claim 13, wherein:

E_gap is a difference between a valence band energy and a conduction band energy; and

the valence band offset is equal to 0.3{E_gap(Al_xhighGa_1-xhighN)−

E_gap(Al_xlowGa_1-xlowN)},

and wherein;

P_x is a total polarization of Al_xGa_1-xN, ∈

_x is a dielectric constant of Al_xGa_1-xN; and

the change in potential within a layer of the SPSL arising from polarization charges at interfaces is equal to T_highT_low(P_xlow−

P_xhigh)/(T_high∈

_xlow+T_low∈

_xhigh).

15. The device of claim 1, wherein the p-type dopant is Mg and the modulation of the valence band edge is greater than 0.35 eV.

16. The device of claim 1, further comprising:

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 the thickness of the p-contact layer.

17. The device of claim 16, wherein:

z is a function of distance, d, over the thickness of the p-contact layer, wherein the thickness of the p-contact layer extends from d=0 at an interface between the p-side heterostructure and the p-contact layer to d=D at an interface between the p-contact layer and the p-contact;

the function z decreases linearly with slope g₁ in a first region extending from d=0 to d=d_mid, wherein d_mid is a point within the p-contact layer between d=0 and d=D; and

the function z decreases linearly with slope g₂ in a second region extending from d=d_mid to d=D, wherein a magnitude of g₂ is greater than a magnitude of g₁.

18. The device of claim 17, wherein a thickness of the SPSL is less than 260 nm and d_mid is greater than 60 nm.

19. The device of claim 16, 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 within the p-contact layer between d=0 and d=D;

z is a function of the distance, d, over the thickness of the p-contact layer, wherein the thickness of the p-contact layer extends from d=0 at the interface between the p-side heterostructure and the p-contact layer to d=D at the interface between the p-contact layer and the p-contact; and

the p-contact layer includes;

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

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

20. The device of claim 1, wherein a lateral resistivity of the SPSL increases by less than a factor of 5 as the temperature T increases from 1000/10 Kelvins to 1000/3 Kelvins.