Method of obtaining planar semipolar gallium nitride surfaces

• US 9,978,845 B2
• Filed: 04/15/2015
• Issued: 05/22/2018
• Est. Priority Date: 04/16/2014
• Status: Active Grant

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Han, Jung, Leung, Benjamin
• Primary Examiner(s): FERNANDES, ERROL V
• Application Number:
  US15/304,189
• Publication Number:
  US 20170033186A1
• Time in Patent Office: 1,133 Days
• CPC Class Codes: H01L 21/0242 Crystalline insulating materials
• CPC Class Codes: H01L 21/0243 Surface structure
• 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 21/02609 Crystal orientation
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 21/02639 Preparation of substrate for selective deposition
• CPC Class Codes: H01L 21/02647 Lateral overgrowth
• CPC Class Codes: H01L 21/30625 With simultaneous mechanical treatment, e.g. mechanico-chemical polishing
• CPC Class Codes: H01L 29/045 by their particular orientation of crystalline planes
• CPC Class Codes: H01L 29/15 Structures with periodic or quasi periodic potential variation, e.g. multiple quantum wells, superlattices such structures applied for the control of light G02F1/017, applied in semiconductor lasers H01S5/34
• CPC Class Codes: H01L 29/155 Comprising only semiconductor materials H01L29/154 takes precedence
• CPC Class Codes: H01L 29/2003 Nitride compounds

Abstract

Methods and structures for forming flat, continuous, planar, epitaxial layers of semipolar III-nitride materials on patterned sapphire substrates are described. Semipolar GaN may be grown from inclined c-plane facets on a patterned sapphire substrate, and coalesced to form a continuous layer of semipolar III-nitride semiconductor over the sapphire substrate. Planarization of the layer is followed by crystal regrowth using a nitrogen carrier gas to produce a flat, microfabrication-grade, process surface of semipolar III-nitride semiconductor across the substrate. Quality multiple quantum wells can be fabricated in the regrown semipolar material.

Claims

1. A method for forming an epitaxial layer of semipolar gallium-nitride on a substrate, the method comprising

growing semipolar gallium-nitride adjacent to crystal-growth surfaces of a patterned sapphire substrate, wherein the crystal-growth surfaces comprise a first portion of a plurality of surfaces of different orientations formed on the patterned sapphire substrate that are not masked by a masking material that masks a remaining second portion of the plurality of surfaces and wherein the crystal-growth surfaces have one select orientation of the different orientations.

2. The method of claim 1, further comprising forming a low-temperature aluminum-nitride or a low-temperature gallium-nitride buffer layer at the crystal-growth surfaces.

3. The method of claim 2, wherein either of the low-temperature buffer layers are formed below a temperature of approximately 600°

C.

4. The method of claim 1, further comprising:

planarizing the grown semipolar gallium-nitride; and

regrowing the semipolar gallium-nitride using a nitrogen carrier gas.

5. The method of claim 4, wherein regrowing the semipolar gallium-nitride comprises regrowth conditions that do not include a hydrogen carrier gas.

6. The method of claim 4, wherein the nitrogen carrier gas is N₂.

7. The method of claim 4, wherein regrowing the semipolar gallium-nitride comprises growing the semipolar gallium-nitride using metal-organic chemical vapor deposition.

8. The method of claim 7, wherein a temperature during regrowth is between approximately 980°

C. and approximately 1070°

C.

9. The method of claim 7, wherein a pressure during regrowth is between approximately 100 mbar and approximately 300 mbar.

10. The method of claim 7, wherein a flow rate of NH₃ gas during regrowth is between approximately 0.5 slm and approximately 4 slm.

11. The method of claim 7, wherein a flow rate of trimethylgallium or triethylgallium during regrowth is between approximately 30 sccm and approximately 50 sccm.

12. The method of claim 7, wherein a growth rate during regrowth is between 1 μ

m/hr and approximately 2 μ

m/hr.

13. The method of claim 4, wherein growing semipolar gallium-nitride and regrowing semipolar gallium-nitride comprise growing the gallium-nitride with a (2021) facet approximately parallel to a process surface of the substrate.

14. The method of claim 4, wherein planarizing the grown semipolar gallium-nitride comprises planarization by chemical-mechanical polishing.

15. The method of claim 4, further comprising, prior to growing semipolar gallium-nitride, forming the masking layer to cover the plurality of surfaces of the patterned sapphire substrate.

16. The method of claim 15, wherein forming the masking layer comprises depositing a material conformally by a vapor deposition process.

17. The method of claim 16, further comprising removing the conformally deposited material from the crystal-growth surfaces.

18. A substrate comprising:

a patterned sapphire substrate having a plurality of surfaces at different orientations and a masking layer formed over all of the plurality of surfaces except crystal-growth surfaces that are a portion of the plurality of surfaces having one select orientation of the different orientations; and

a semipolar gallium-nitride epitaxial layer formed over the patterned sapphire substrate.

19. The substrate of claim 18, wherein the patterned sapphire substrate has a (2243) facet approximately parallel to a process surface of the substrate and a c-plane facet approximately parallel to the crystal-growth surfaces.

20. The substrate of claim 18, wherein the patterned sapphire substrate comprises an array of trenches with the crystal-growth surfaces forming inclined walls of the trenches.

21. The substrate of claim 20, wherein a spacing of the trenches is between approximately 0.25 microns and approximately 10 microns, and a depth of the trenches is between approximately 50 nanometers and approximately 2 microns.

22. The substrate of claim 20, wherein the epitaxial gallium-nitride layer coalesces above the trenches to form a continuous and planar semiconductor layer across the substrate.

23. The substrate of claim 22, wherein a roughness of a surface of the planer semiconductor layer measured over a 15 μ

m×

15 μ

m area is less than 5 nm root-mean-square.

24. The substrate of claim 18, further comprising a buffer layer between the crystal-growth surfaces and the epitaxial gallium-nitride.

25. The substrate of claim 24, wherein the buffer layer comprises aluminum-nitride.

26. The substrate of claim 22, wherein the planar semipolar gallium-nitride epitaxial layer has a single and continuous planar surface across the substrate that is approximately parallel to a (2021) facet of the semipolar gallium-nitride.