Method of preparing and storing GaN substrate, prepared and stored GaN substrate, and semiconductor device and method of its manufacture

1. A GaN substrate preparation and storage method comprising:

a substrate-preparation step of preparing a GaN substrate, defining first and second principal faces as distinct from the substrate edge, so as to have a planar first principal face and a plane orientation, in an arbitrary point along the first principal face and separated 3 mm or more from the outer edge thereof, having an off-inclination angle of between −10° and 10°, inclusive, with respect to the plane orientation of an arbitrarily designated crystalline plane that is inclined between 50° and 90°, inclusive, with respect to a plane, being either the (0001) plane or the (000 1 ) plane, through the arbitrary point;

a storage-atmosphere preparation step of preparing a GaN-substrate storage atmosphere of not greater than 15 vol. % oxygen concentration and not greater than 20 g/m 3 water-vapor concentration; and

a storage step of storing the prepared GaN substrate within the atmosphere prepared in said storage-atmosphere preparation step.

2. The GaN substrate preparation and storage method set forth in claim 1 , wherein in said storage-atmosphere preparation step, the atmosphere is prepared to have an oxygen concentration of not greater than 10 vol. % and a water-vapor concentration of not greater than 15 g/m 3 .

3. The GaN substrate preparation and storage method set forth in claim 1 , wherein in said storage-atmosphere preparation step, the atmosphere is prepared to have an oxygen concentration of not greater than 6 vol. % and a water-vapor concentration of not greater than 5 g/m 3 .

4. The GaN substrate preparation and storage method set forth in claim 1 , wherein in said storage-atmosphere preparation step, the atmosphere is prepared by forming the atmosphere from a gaseous mixture containing an inert gas, gaseous oxygen, and water vapor, and such that the oxygen concentration is not less than 0.05 vol. % and the water-vapor concentration is not less than 0.1 g/m 3 .

5. The GaN substrate preparation and storage method set forth in claim 1 , wherein in substrate-preparation step, the GaN substrate is prepared so as to have a first-principal-face average roughness Ra of 20 nm or less, and a second-principal-face average roughness Ra of 20 μm or less.

6. The GaN substrate preparation and storage method set forth in claim 1 , wherein in substrate-preparation step, the GaN substrate is prepared so as to have a first-principal-face average roughness Ra of 5 nm or less, and a second-principal-face average roughness Ra of 10 μm or less.

7. The GaN substrate preparation and storage method set forth in claim 1 , wherein in said substrate-preparation step the plane orientation of the arbitrarily designated crystalline plane, with respect to which the first-principal-face arbitrary-point plane orientation of the GaN substrate is made to be off-angled, is {20 2 1}.

8. The GaN substrate preparation and storage method set forth in claim 7 , wherein in said substrate-preparation step the first-principal-face arbitrary-point plane orientation of the GaN substrate is made to be off-angled between −10° and 10°, inclusive, in a <1 2 10> direction with respect to {20 2 1}, and between −10° and 10°, inclusive, in a direction perpendicular to a <20 2 1> direction and to a <1 2 10> direction.

9. The GaN substrate preparation and storage method set forth in claim 7 , wherein in said substrate-preparation step the first-principal-face arbitrary-point plane orientation of the GaN substrate is made to be off-angled between −3° and 3°, inclusive, in a <1 2 10> direction with respect to {20 2 1}, and between −3° and 3°, inclusive, in a direction perpendicular to a <20 2 1> direction and to a <1 2 10> direction.

10. The GaN substrate preparation and storage method set forth in claim 7 , wherein in said substrate-preparation step the first-principal-face arbitrary-point plane orientation of the GaN substrate is made to be off-angled between −0.5° and 0.5°, inclusive, in a <1 2 10> direction with respect to {20 2 1}, and between −0.5° and 0.5°, inclusive, in a direction perpendicular to a <20 2 1> direction and to a <1 2 10> direction.

11. A GaN substrate stored within an atmosphere in which the oxygen concentration is not greater than 15 vol. % and the water-vapor concentration is not greater than 20 g/m 3 , having a planar first principal face, and whose plane orientation in an arbitrary point along the first principal face and separated 3 mm or more from the outer edge thereof has an off-inclination angle of between −10° and 10°, inclusive, with respect to the plane orientation of an arbitrarily designated crystalline plane that is inclined between 50° and 90°, inclusive, with respect to a plane, being either the (0001) plane or the (000 1 ) plane, through the arbitrary point.

12. A semiconductor device including a GaN substrate of claim 11 , and an at least single-lamina semiconductor layer formed onto the first principal face of the GaN substrate.

13. A semiconductor device manufacturing method comprising:

a step of obtaining a GaN substrate prepared and stored according to the method of claim 1 ; and

a step of growing an at least single-lamina semiconductor layer onto the first principal face of the GaN substrate.