Thick pseudomorphic nitride epitaxial layers

• US 9,437,430 B2
• Filed: 01/25/2008
• Issued: 09/06/2016
• 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: Schowalter, Leo J., Smart, Joseph A., Grandusky, James R., Liu, Shiwen
• Primary Examiner(s): Jackson, Jr., Jerome
• Application Number:
  US12/020,006
• Publication Number:
  US 20080187016A1
• Time in Patent Office: 3,147 Days
• US Class Current: 1/1
• CPC Class Codes: H01L 21/02389 Nitrides
• 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 21/0251 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 33/08 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

Abstract

Semiconductor structures are fabricated to include strained epitaxial layers exceeding a predicted critical thickness thereof.

Claims

1. A semiconductor heterostructure comprising:

an aluminum nitride single-crystal substrate; and

at least one strained layer epitaxially grown thereover, the layer comprising at least one of AlN, GaN, InN, or any binary or tertiary alloy combination thereof,

wherein a thickness of the strained layer exceeds a predicted critical thickness associated therewith by at least a factor of 5, as calculated with the Matthews-Blakeslee theory,

2. The semiconductor heterostructure of claim 1, wherein the thickness of the at least one strained layer exceeds the predicted critical thickness by at least a factor of 10.

3. The semiconductor heterostructure of claim 1, wherein the at least one strained layer is substantially free of In.

4. The semiconductor heterostructure of claim 1, wherein the at least one strained layer has a density of macroscopic defects less than approximately 1 mm⁻

2.

5. The semiconductor heterostructure of claim 1, wherein a strain parallel to the at least one strained layer is greater than 80% of a difference between parallel lattice parameters of an unstrained alloy of the same composition as the at least one strained layer and a relaxed platform disposed beneath the at least one strained layer.

6. The semiconductor heterostructure of claim 5, wherein the at least one strained layer comprises Al_xGa_1-xN, the thickness of the at least one strained layer is greater than approximately 200 nm, and x is less than approximately 0.65.

7. The semiconductor heterostructure of claim 1, wherein the thickness of the at least one strained layer is greater than approximately 1 μ

m.

8. The semiconductor heterostructure of claim 1, wherein the at least one strained layer has an average threading dislocation density less than approximately 10,000 cm⁻

2.

23. The semiconductor heterostructure of claim 1, further comprising a relaxed cap layer disposed over the at least one strained layer.

9. A method for forming a semiconductor heterostructure, the method comprising:

providing an aluminum nitride single-crystal substrate; and

epitaxially depositing over the substrate a strained layer comprising at east one of AlN, GaN, InN, or any binary or tertiary alloy combination thereof,

wherein a thickness of the strained layer exceeds a predicted critical thickness associated therewith by at least a factor of 5, as calculated with the Matthews-Blakeslee theory,

10. The method of claim 9, further comprising forming a buffer layer over the substrate prior to depositing the strained layer.

11. The method of claim 10, further comprising forming a graded layer between the buffer layer and the strained layer.

12. The method of claim 9, wherein the thickness of the strained layer exceeds the predicted critical thickness by at least a factor of 10.

13. The method of claim 9, wherein the strained layer is substantially free of In.

14. The method of claim 9, wherein the strained layer has a density of macroscopic defects less than approximately 1 mm⁻

2.

15. The method of claim 9, wherein the strained layer comprises AlGaN, and epitaxially depositing the strained layer comprises introducing trimethylaluminum and trimethylgallium into a reactor.

16. The method of claim 15, wherein an initial flow rate of the trimethylgallium during the deposition of the strained layer is lower than a final trimethylgallium flow rate.

17. The method of claim 9, wherein the aluminum nitride single-crystal substrate has an RMS surface roughness less than approximately 0.5 nm for a 10 μ

m×

10 μ

m area, a surface misorientation between approximately 0.3° and

4°

, and a threading dislocation density less than approximately 10⁴ cm<sup>−

2</sup>.

18. The method of claim 9, wherein a threading dislocation density of the strained layer is approximately equal to a threading dislocation density of the aluminum nitride single crystal substrate.

24. The method of claim 9, further comprising forming over the strained layer a relaxed cap layer, the strained layer remaining strained after formation of the relaxed cap layer.

25. The method of claim 9, further comprising heating the substrate to approximately 1100°

C. prior to epitaxially depositing the strained layer.

26. The method of claim 9, wherein the strained layer is epitaxially deposited at a temperature ranging from greater than approximately 1100°

C. to approximately 1300°

C.

19. A device selected from the group consisting of a field effect transistor, a light-emitting diode, and a laser diode, the device comprising at least a portion of a strained heterostructure including:

an aluminum nitride single-crystal substrate; and

at least one strained layer epitaxially grown thereover, the layer comprising at least one of AlN, GaN, InN, or any binary or tertiary alloy combination thereof,

wherein a thickness of the strained layer exceeds a predicted critical thickness associated therewith by at least a factor of 10, as calculated with the Matthews-Blakeslee theory,

20. The device of claim 19, wherein the device is a light-emitting diode comprising at least one interdigitated contact.

27. The device of claim 19, further comprising a relaxed cap layer disposed over the at least one strained layer.

21. A device selected from the group consisting of a field effect transistor, a light-emitting diode, and a laser diode, the device comprising at least a portion of a strained heterostructure including:

an aluminum nitride single-crystal substrate; and

a plurality of strained layers epitaxially grown thereover, each of the plurality of strained layers comprising at least one of AlN, GaN, InN, or any binary or tertiary alloy combination thereof,

wherein a total thickness of the plurality of strained layers exceeds a predicted critical thickness associated therewith by at least a factor of 10, as calculated with the Matthews-Blakeslee theory,

22. The device of claim 21, wherein a lattice parameter parallel to the surface of the aluminum nitride single-crystal substrate of each of the plurality of strained layers is different from a lattice parameter of the aluminum nitride single-crystal substrate by less than 0.2%.

28. The device of claim 21, further comprising a relaxed cap layer disposed over the plurality of strained layers.