P-side layers for short wavelength light emitters

• US 10,164,146 B2
• Filed: 07/13/2016
• Issued: 12/25/2018
• 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:
  US15/209,715
• Publication Number:
  US 20160336481A1
• Time in Patent Office: 895 Days
• 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) 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 p-side heterostructure and the n-side heterostructure;

a metallic p-contact; and

a p-contact layer disposed between the SPSL and the metallic p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z varies with respect to distance, d, in the p-contact layer, such that z decreases continuously and linearly with slope g₁ in a first region extending from d =0 at an interface between the SPSL and the p-contact layer to d =d_mid; and

z decreases continuously and 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 metallic p-contact, wherein a magnitude of g₂ is different from a magnitude of g₁,

wherein the alternating layers cause modulation in a valence band potential in the SPSL and the modulation is at least equal to an acceptor level energy of the p-type dopant, and wherein the p-type dopant is Mg and the modulation is greater than 0.35 eV.

2. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) comprising alternating layers of Al_xhighGa_1-xhighN and Al_xlowGa_1-xlowN;

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 SPSL of the p-side heterostructure and the metallic p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z is a nonlinear function with respect to distance, d, in the p-contact layer, wherein d=0 at an interface between the SPSL and the p-contact layer and d=D at an interface between the p-contact layer and the metallic p-contact and there is at least one inflection point at d=d_w in the nonlinear continuous function of z with respect to d between d=0 and d=D.

3. The device of claim 2, wherein:

the nonlinear function of z with respect to d comprises;

a first nonlinear portion between d=0 and d=d_w; and

a second nonlinear portion between d=d_w and d=D.

4. The device of claim 3, wherein d_w is greater than 30% of the thickness, D, of the p-contact layer.

5. The device of claim 4, wherein D is 100 nm.

6. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) comprising alternating layers of Al_xhighGa_1-xhighN and Al_xlowGa_1-xlowN;

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 SPSL superlattice and the metallic p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z is a nonlinear function with respect to distance, d, in the p-contact layer, wherein d=0 at an interface between the SPSL and the p-contact layer and d=D at an interface between the p-contact layer and the metallic p-contact and there is at least one inflection point at d=d_w in the nonlinear function of z with respect to d between d=0 and d=D, wherein z decreases from 0.7 proximate to the SPSL to 0 proximate to the metallic p-contact.

7. 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 SPSL of the p-side heterostructure and the metallic p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z varies with respect to distance, d, in the p-contact layer, such that z decreases linearly with slope g₁ in a first region extending from d=0 at an interface between the SPSL 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 metallic p-contact, wherein a magnitude of g₂ is different from a magnitude of g₁.

8. The device of claim 7, wherein the alternating layers cause modulation in a valence band potential in the SPSL and the modulation is at least equal to an acceptor level energy of the p-type dopant.

9. The device of claim 7, wherein a thickness of each of the alternating layers is less than or equal to six AlGaN bi-layers, 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.

10. The device of claim 7, wherein a thickness of the SPSL is less than 260 nm and d_mid is greater than 60 nm.

11. The device of claim 7, 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 p-doped Al_x1highGa_1-x1highN and p-doped Al_x1lowGa_1-x1lowN, the second portion comprising a second number of alternating layers of p-doped Al_x2highGa_1-x2highN and p-doped Al_x2lowGa_1-x2lowN, and wherein a thickness of 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.

12. The device of claim 11, wherein X_2low≤

x_2high≤

0.9.

13. The device of claim 11, wherein at least some layers of the first portion have a thickness greater than a thickness of the layers of the second portion.

14. A light emitting device, comprising:

a p-side heterostructure comprising a short period superlattice (SPSL) comprising alternating layers of Al_xhighGa_1-xhighN and Al_xlowGa_1-xlowN;

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 SPSL and the metallic p-contact, the p-contact layer comprising Al_zGa_1-zN and having a thickness, D, where z is a nonlinear function with respect to distance, d, in the p-contact layer, wherein d=0 at an interface between the SPSL and the p-contact layer and d=D at an interface between the p-contact layer and the metallic p-contact and there is at least one inflection point at d=d_w in the nonlinear function of z with respect to d between d=0 and d=D, wherein the thickness of the SPSL is less than 260 nm and d_w is greater than 60 nm.