GaN single-crystal substrate, nitride type semiconductor epitaxial substrate, nitride type semiconductor device, and methods of making the same

• US 20030209185A1
• Filed: 05/08/2003
• Published: 11/13/2003
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: Institute of Materials Research and Engineering, Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Original Assignee: Institute of Materials Research and Engineering, Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Inventors: Ueno, Masaki, Chen, Peng, Takasuka, Eiryo, Chua, Soo-Jin
• Granted Patent: US 6,841,274 B2
• Time in Patent Office: Days
• US Class Current: 117/2
• CPC Class Codes: C30B 25/02 Epitaxial-layer growth
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/02658 Pretreatments cleaning in general H01L21/02041
• CPC Class Codes: H01L 21/3245 of AIIIBV compounds
• CPC Class Codes: H01L 21/3247 for altering the shape, e.g. smoothing the surface

Abstract

The GaN single-crystal substrate 11 in accordance with the present invention has a polished surface subjected to heat treatment for at least 10 minutes at a substrate temperature of at least 1020° C. in a mixed gas atmosphere containing at least an NH₃ gas. As a consequence, an atomic rearrangement is effected in the surface of the substrate 11 in which a large number of minute defects are formed by polishing, so as to flatten the surface of the substrate 11. Therefore, the surface of an epitaxial layer 12 formed on the substrate 11 can be made flat.

Claims

1. A GaN single-crystal substrate having a polished surface flattened by heat treatment for at least 10 minutes at a substrate temperature of at least 1020°

C. in a mixed gas atmosphere containing at least an NH₃ gas.

2. A GaN single-crystal substrate according to claim 1, wherein said surface exhibits a root-mean-square roughness of 0.2 nm or less after said heat treatment.

3. A nitride type semiconductor epitaxial substrate comprising the GaN single-crystal substrate according to claim 1, and a nitride type compound semiconductor layer epitaxially grown on said GaN single-crystal substrate.

4. A nitride type semiconductor epitaxial substrate according to claim 3, wherein said nitride type compound semiconductor layer comprises Al_xGa_yIn₁₋

x−

yN (0≦

x ≦

1, 0≦

y≦

1, x+y≦

1).

5. A nitride type semiconductor epitaxial substrate according to claim 3, wherein said nitride type compound semiconductor layer comprises GaN.

6. A nitride type semiconductor epitaxial substrate according to one of claims 3, wherein said nitride type compound semiconductor layer epitaxially grown on said GaN single-crystal substrate has a surface with a root-mean-square roughness of 0.2 nm or less.

7. A nitride type semiconductor epitaxial substrate according to one of claims 3, wherein said nitride type compound semiconductor layer has an x-ray diffraction half width of 100 seconds or less.

8. A nitride type semiconductor epitaxial substrate according to one of claims 3, wherein said nitride type compound semiconductor layer has a threading dislocation density of 1×

10⁶ cm<sup>−

2</sup> or less.

9. A nitride type semiconductor device comprising the GaN single-crystal substrate according to claim 1, said substrate having an n-type conductivity;

an n-type cladding layer, laminated on said substrate, comprising Al_xGa<sub>1−

x</sub>N (0<

x<

1);

an active layer laminated on said cladding layer;

a p-type cladding layer, laminated on said active layer, comprising Al_xGa<sub>1−

x</sub>N (0<

x<

1); and

a p-type GaN layer laminated on said p-type cladding layer.

10. A nitride type compound semiconductor device comprising the GaN single-crystal substrate according to claim 1, and a plurality of nitride type semiconductor layers laminated on said substrate and represented by Al_xGa_yIn₁₋

x−

yN (0≦

x≦

1, 0≦

y≦

1, x+y≦

1).

11. A GaN single-crystal substrate having a surface with a root-mean-square roughness of 0.2 nm or less.

12. A method of making a GaN single-crystal substrate, said method comprising the step of subjecting a GaN single-crystal having a polished surface to heat treatment for at least 10 minutes at a substrate temperature of at least 1020°

C. in a mixed gas atmosphere containing at least an NH₃ gas, so that said surface of said GaN single-crystal substrate has a root-mean-square roughness of 0.2 nm or less.

13. A method of making a GaN single-crystal substrate according to claim 12, wherein said mixed gas contains an H₂ gas.

14. A method of making a nitride type semiconductor epitaxial substrate, said method comprising the step of epitaxially growing a nitride type compound semiconductor layer on said GaN single-crystal substrate obtained by the method of making a GaN single-crystal substrate according to claim 12 without oxidizing said surface of said GaN single-crystal substrate.

15. A method of making a nitride type semiconductor epitaxial substrate according to claim 14, wherein said nitride type compound semiconductor layer is of n type.

16. A method of making a nitride type semiconductor epitaxial substrate according to claim 14, wherein said nitride type compound semiconductor layer is of p type.

17. A method of making a nitride type semiconductor epitaxial substrate according to one of claims 14, wherein said epitaxial growth utilizes one of OMVPE, HVPE, and MBE.

18. A method of making a nitride type semiconductor epitaxial substrate according to one of claims 14, wherein both said heat treatment of said GaN single-crystal substrate and said epitaxial growth are effected within an apparatus for carrying out said epitaxial growth.

19. A method of making a nitride type semiconductor device comprising the steps of laminating an n-type cladding layer comprising Al_xGa₁₋

xN (0<

x<

1) on the GaN single-crystal obtained by the method of making a GaN single-crystal substrate according to claim 12, said substrate having an n-type conductivity;

laminating an active layer on said cladding layer;

laminating a p-type cladding layer comprising Al_xGa<sub>1−

x</sub>N (0<

x<

1) on said active layer; and

laminating a p-type GaN layer on said p-type cladding layer.

20. A method of making a nitride type semiconductor device comprising the step of forming a plurality of nitride type semiconductor layers represented by Al_xGa_yIn₁₋

x−

yN (0≦

x≦

1, 0≦

y≦

1, x+y≦

1) and laminated on the GaN single-crystal substrate obtained by the method of making a GaN single-crystal substrate according to claim 12.