Pseudomorphic electronic and optoelectronic devices having planar contacts

• US 9,299,880 B2
• Filed: 03/13/2014
• Issued: 03/29/2016
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Original Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Inventors: Grandusky, James R., Schowalter, Leo J., Jamil, Muhammad, Mendrick, Mark C., Gibb, Shawn R.
• Primary Examiner(s): Stark, Jarrett
• Assistant Examiner(s): Ausar-El, Charles N
• Application Number:
  US14/208,379
• Publication Number:
  US 20140264263A1
• Time in Patent Office: 747 Days
• Field of Search: 257/13
• US Class Current: 1/1
• CPC Class Codes: H01L 2933/0016 relating to electrodes
• CPC Class Codes: H01L 2933/0025 relating to coatings
• CPC Class Codes: H01L 2933/0058 relating to optical field-shaping elements
• 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 33/12 with a stress relaxation structure, e.g. buffer layer
• 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 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/325 characterised by the doping materials
• CPC Class Codes: H01L 33/387 with a plurality of electrode regions in direct contact with the semiconductor body and being electrically interconnected by another electrode layer
• CPC Class Codes: H01L 33/40 Materials therefor
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/42 Transparent materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

In various embodiments, light-emitting devices incorporate smooth contact layers and polarization doping (i.e., underlying layers substantially free of dopant impurities) and exhibit high photon extraction efficiencies.

Claims

1. An ultraviolet (UV) light-emitting device comprising:

a substrate having an Al_yGa_1-yN top surface, wherein y≧

0.4;

a light-emitting device structure disposed over the substrate, the device structure comprising a plurality of layers each comprising Al_xGa_1-xN;

an undoped graded Al_1-zGa_zN layer disposed over the device structure, a composition of the graded layer being graded in Ga concentration z such that the Ga concentration z increases in a direction away from the light-emitting device structure;

a p-doped Al_1-wGa_wN cap layer disposed over the graded layer, the p-doped Al_1-wGa_wN cap layer having (i) a thickness between approximately 2 nm and approximately 30 nm, (ii) a surface roughness of less than approximately 6 nm over a sample size of approximately 200 μ

m×

300 μ

m, and (iii) a Ga concentration w≧

0.8; and

a metallic contact disposed over the Al_1-wGa_wN cap layer and comprising at least one metal, the metallic contact having a contact resistivity to the Al_1-wGa_wN cap layer of less than approximately 1.0 mΩ

-cm².

2. The light-emitting device of claim 1, wherein the Al_1-wGa_wN cap layer is doped with Mg.

3. The light-emitting device of claim 1, wherein the Al_1-wGa_wN cap layer is at least partially relaxed.

4. The light-emitting device of claim 1, wherein the light-emitting device has a photon extraction efficiency of greater than 25%.

5. The light-emitting device of claim 1, wherein the graded layer and Al_1-wGa_wN cap layer collectively absorb less than 80% of UV photons generated by the light-emitting device structure and having a wavelength less than 340 nm.

6. The light-emitting device of claim 1, wherein the at least one metal of the metallic contact comprises Ni/Au or Pd.

7. The light-emitting device of claim 1, wherein the metallic contact has a reflectivity to light generated by the light-emitting device structure of approximately 60% or less.

8. The light-emitting device of claim 1, wherein the metallic contact has a reflectivity to light generated by the light-emitting device structure of approximately 30% or less.

9. The light-emitting device of claim 1, wherein the metallic contact has the form of a plurality of discrete lines and/or pixels of the at least one metal, portions of the Al_1-wGa_wN cap layer not being covered by the metallic contact.

10. The light-emitting device of claim 9, further comprising a reflector disposed over the metallic contact and the uncovered portions of the Al_1-wGa_wN cap layer.

11. The light-emitting device of claim 10, wherein the reflector comprises a metal having greater than 90% reflectivity to UV light and a work function less than approximately 4.5 eV.

12. The light-emitting device of claim 10, wherein the reflector has a contact resistivity to the Al_1-wGa_wN cap layer of greater than approximately 5 mΩ

-cm².

13. The light-emitting device of claim 10, wherein the reflector has a contact resistivity to the Al_1-wGa_wN cap layer of greater than approximately 10 mΩ

-cm².

14. The light-emitting device of claim 10, wherein the reflector comprises Al.

15. The light-emitting device of claim 1, wherein the light-emitting device comprises a light-emitting diode.

16. The light-emitting device of claim 1, wherein (i) a bottom portion of the graded layer proximate the active device structure has a Ga concentration z substantially equal to a Ga concentration of a layer directly thereunder and (ii) a top portion of the graded layer opposite the bottom portion of the graded layer has a Ga concentration z of approximately 1.

17. The light-emitting device of claim 1, wherein the substrate consists essentially of doped or undoped AlN.