Thick pseudomorphic nitride epitaxial layers

• US 10,446,391 B2
• Filed: 11/17/2011
• Issued: 10/15/2019
• Est. Priority Date: 01/26/2007
• 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., Gibb, Shawn R., Smart, Joseph A., Liu, Shiwen
• Primary Examiner(s): Kim, Jay C
• Application Number:
  US13/298,570
• Publication Number:
  US 20120104355A1
• Time in Patent Office: 2,889 Days
• Field of Search: 257 12
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: H01L 21/02433 Crystal orientation
• CPC Class Codes: H01L 21/02458 Nitrides
• 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 33/025 Physical imperfections, e.g. particular concentration or distribution of impurities
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H01L 33/12 with a stress relaxation structure, e.g. buffer layer
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

In various embodiments, a semiconductor device includes an aluminum nitride single-crystal substrate, a pseudomorphic strained layer disposed thereover that comprises at least one of AlN, GaN, InN, or an alloy thereof, and, disposed over the strained layer, a semiconductor layer that is lattice-mismatched to the substrate and substantially relaxed.

Claims

1. A light-emitting device comprising:

a single-crystal aluminum nitride substrate having opposed top and bottom surfaces;

disposed over the top surface of the substrate, a strained bottom contact layer comprising doped Al_nGa_1-nN, n being less than 1, wherein the strained bottom contact layer is pseudomorphically strained with respect to the substrate, such that the strained bottom contact layer is less than 20% relaxed to its innate lattice parameter;

disposed over the bottom contact layer, a multiple-quantum well layer comprising a plurality of periods each comprising a strained Al_xGa_1-xN barrier and a strained Al_yGa_1-yN quantum well, wherein (i) x and y are different by an amount facilitating confinement of electrons and holes in the multiple-quantum well layer and (ii) y is selected such that an emission wavelength of the light-emitting device is in the range of 210 nm to 320 nm;

disposed over the multiple-quantum well layer, a doped top contact layer comprising Al_zGa_1-zN providing electrical contact to at least one layer therebelow; and

disposed over the top contact layer, a metallic contact layer.

2. The device of claim 1, further comprising, disposed between the top surface of the substrate and the bottom contact layer, a strained graded Al_mGa_1-mN layer, the composition of the strained graded Al_mGa_1-mN layer being graded over its thickness from a value of m being approximately equal to 1 to a value of m being approximately equal to n, wherein the strained graded Al_mGa_1-mN layer is pseudomorphically strained with respect to the substrate, such that the strained graded Al_mGa_1-mN layer is less than 20% relaxed.

3. The device of claim 2, further comprising a homoepitaxial AlN layer disposed between the top surface of the substrate and the graded Al_mGa_1-mN layer.

4. The device of claim 1, wherein an angle between a c-axis and a surface normal of the substrate has a value ranging between 0.3°

and 4°

.

5. The device of claim 4, wherein the angle is approximately 1°

.

6. The device of claim 1, wherein x and y differ by an amount ranging from approximately 0.05 to approximately 0.3.

7. The device of claim 1, wherein the substrate has a density of particulate surface defects less than approximately 100 cm⁻

2.

8. The device of claim 1, wherein the top contact layer is pseudomorphically strained with respect to the substrate, such that the top contact layer is less than 20% relaxed to its innate lattice parameter.

9. The device of claim 1, further comprising a cap layer disposed between the top contact layer and the metallic contact layer, the cap layer comprising one or more semiconductor materials doped with a conductivity the same as a conductivity with which the top contact layer is doped.

10. The device of claim 9, wherein the cap layer is lattice-mismatched to the substrate and substantially relaxed to its unstrained lattice constant.

11. The device of claim 9, wherein the cap layer comprises a plurality of coalesced islands.

12. The device of claim 9, wherein the cap layer comprises GaN.

13. The device of claim 9, further comprising an array of misfit dislocations disposed at an interface between the cap layer and the top contact layer.

14. The device of claim 1, wherein the bottom surface of the substrate comprises a plurality of tapered structures for improving photon extraction efficiency.

15. The device of claim 9, further comprising an electron-blocking layer disposed between the multiple-quantum well layer and the top contact layer, the electron-blocking layer comprising doped aluminum gallium nitride.

16. The device of claim 1, wherein the top contact layer is doped p-type, the metallic contact layer making direct physical contact with the top contact layer.

17. The device of claim 9, wherein the cap layer is doped p-type, the metallic contact layer making electrical contact with the top contact layer.

18. The device of claim 1, wherein a thickness of the bottom contact layer is less than 200 nm.

19. The device of claim 1, wherein the metallic contact layer comprises an ultraviolet reflector for redirecting light emitted by the multiple-quantum well layer toward the substrate.

20. The device of claim 1, wherein (i) z>

0 and (ii) the top contact layer is in direct physical contact with the metallic contact layer.