Nitride semiconductor substrate and its production method
A nitride semiconductor substrate having a diameter of 10 mm or more, which has a single-layer structure composed of a nitride semiconductor layer having a basic composition represented by Al x Ga 1−x N (0≦x≦1), or a multi-layer structure comprising the nitride semiconductor layer, the mass density of the nitride semiconductor layer being 98% or more of a theoretical mass density ρ (x) represented by the following general formula (1): ρ ( x ) = 4 ( M x + M N ) 3 a x 2 c x N a , ( 1 ) wherein a x =a GaN +(a AlN −a GaN )x, wherein a GaN represents an a-axis length of GaN, and a AlN represents an a-axis length of AlN; c x =c GaN +(c AlN −c GaN )x, wherein c GaN represents a c-axis length of GaN, and C AlN represents a c-axis length of AlN; M x =M Ga +(M Al −M Ga )x, wherein M Ga represents the atomic weight of Ga, and M Al represents the atomic weight of Al; M N represents the atomic weight of nitrogen; and N a represents Avogadro's number.
1. A nitride semiconductor substrate having a diameter of 10 mm or more comprising a nitride semiconductor layer having a basic composition represented by Al x Ga 1−x N (0≦x≦1), the mass density of said nitride semiconductor layer being 98% or more of a theoretical mass density ρ (x) represented by the following general formula (1):
ρ
(
x
)
=
4
(
M
x
+
M
N
)
3
a
x
2
c
x
N
a
,
(
1
)
wherein a x =a GaN +(a AlN −c GaN )x, wherein c GaN represents an a a-axis length of GaN, and a AlN represents an a-axis length of AlN; c x =c GaN +(C AlN −c GaN )x, wherein c GaN represents a c-axis length of GaN, and C AlN represents a c-axis length of AlN; M x =M Ga +(M Al −M Ga )x, wherein M Ga represents the atomic weight of Ga, and M Al represents the atomic weight of Al; M N represents the atomic weight of nitrogen; and N a represents Avogadro's number.
2. The nitride semiconductor substrate according to claim 1 , wherein it is a self-supported substrate composed of said nitride semiconductor layer.
3. The nitride semiconductor substrate according to claim 2 , wherein said nitride semiconductor layer has a thickness of 200 μm or more.
4. The nitride semiconductor substrate according to claim 1 , wherein a distribution of said mass density is within ±0.1% in a plane.
5. The nitride semiconductor substrate according to claim 1 , wherein a distribution of said mass density is within ±0.2% in a thickness direction.
6. The nitride semiconductor substrate according to claim 1 , wherein said nitride semiconductor layer is composed of a single crystal.
7. The nitride semiconductor substrate according to claim 1 , wherein said nitride semiconductor layer has a threading edge dislocation density of 1×10 7 cm 2 or less.
8. A method for producing the nitride semiconductor substrate according to claim 1 , wherein said nitride semiconductor layer is grown by a hydride vapor-phase epitaxy method.
9. The method for producing a nitride semiconductor substrate according to claim 8 , wherein a nitrogen compound gas used as a starting material for said nitride semiconductor layer has a partial pressure of 50 kPa or more.
10. The method for producing a nitride semiconductor substrate according to claim 8 , wherein said nitride semiconductor layer is epitaxially grown on a different substrate.
11. The method for producing a nitride semiconductor substrate according to claim 10 , wherein the epitaxially grown nitride semiconductor layer is separated from the different substrate to provide a self-supported substrate of a nitride semiconductor.
12. The method for producing a nitride semiconductor substrate according to claim 8 , wherein after said nitride semiconductor layer is epitaxially grown, a heat treatment is conducted in an atmosphere containing a nitrogen compound gas.
13. The method for producing a nitride semiconductor substrate according to claim 12 , wherein said heat treatment is conducted at a pressure of 4 MPa or more.
14. The method for producing a nitride semiconductor substrate according to claim 12 , wherein a heat treatment temperature is 400–1200° C.
15. The nitride semiconductor substrate according to claim 1 , said nitride semiconductor layer being grown by a hydride vapor-phase epitaxy method.
16. The nitride semiconductor substrate according to claim 15 , wherein a nitrogen compound gas used as a starting material for said nitride has a partial pressure of 50 kPa or more.
17. The nitride semiconductor substrate according to claim 15 , wherein said nitride semiconductor layer is epitaxially grown on a different substrate.
18. The nitride semiconductor substrate according to claim 17 , wherein the epitaxially grown nitride semiconductor layer is separated from the different substrate to provide a self-supported substrate of a nitride semiconductor.
19. The nitride semiconductor substrate according to claim 15 , wherein after said nitride semiconductor layer is epitaxially grown, a heat treatment is conducted in an atmosphere containing a nitrogen compound gas.
20. The nitride semiconductor substrate according to claim 19 , wherein said heat treatment is conducted at a pressure of 4 MPa or more.
21. The nitride semiconductor substrate according to claim 19 , wherein a heat treatment temperature is 400–1200° C.