Group III nitride semiconductor multilayer structure and production method thereof
According to the present invention, an AlN crystal film seed layer having high crystallinity is combined with selective/lateral growth, whereby a Group III nitride semiconductor multilayer structure more enhanced in crystallinity can be obtained. The Group III nitride semiconductor multilayer structure of the present invention is a Group III nitride semiconductor multilayer structure where an AlN crystal film having a crystal grain boundary interval of 200 nm or more is formed as a seed layer on a C-plane sapphire substrate surface by a sputtering method and an underlying layer, an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer, each composed of a Group III nitride semiconductor, are further stacked, wherein regions in which the seed layer is present and is absent are formed on the C-plane sapphire substrate surface and/or regions capable of epitaxial growth and incapable of epitaxial growth are formed in the underlying layer.
1. A production method of a Group III nitride semiconductor multilayer structure, comprising producing a Group III nitride semiconductor multilayer structure where an AlN crystal film having a crystal grain boundary interval of 200 nm or more is formed as a seed layer on a C-plane sapphire substrate surface by a sputtering method and an underlying layer, an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer, each composed of a Group III nitride semiconductor, are further stacked, wherein (A) regions in which said seed layer is present and is absent are formed on said C-plane sapphire substrate surface and/or (B) regions capable of epitaxial growth and incapable of epitaxial growth are formed in said underlying layer.
2. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the seed layer-free region on the C-plane sapphire substrate surface is formed in a stripe or island/sea fashion having periodicity.
3. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the seed layer-free region on the C-plane sapphire substrate surface is obtained by growing an AlN crystal film as a seed layer on the C-plane sapphire substrate layer and then removing by etching a part of the AlN crystal film.
4. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the seed layer-free region on the C-plane sapphire substrate surface is obtained by forming regions allowing and disallowing the seed layer of the C-plane to grow on the sapphire substrate surface and then growing an AlN crystal film as a seed layer only in the region allowing growth of the seed layer.
5. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 4 , wherein the region disallowing growth of the seed layer is formed using either one of the following methods (α) and (β):
(α) said C-plane sapphire substrate surface is processed to provide a region in a stripe or island/sea fashion having periodicity and thereby form a plane other than C-plane, and
(β) a region in a stripe or island/sea fashion having periodicity is covered with amorphous SiO 2 , amorphous silicon nitride or a high melting-point metal.
6. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the region incapable of epitaxial growth in the underlying layer is formed by either one of the following methods (γ) and (δ):
(γ) said C-plane sapphire substrate surface is processed to provide a region in a stripe or island/sea fashion having periodicity and thereby form a plane other than C-plane, and
(δ) a region in a stripe or island/sea fashion having periodicity is covered with amorphous SiO 2 , amorphous silicon nitride or a high melting-point metal.
7. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the full width at half maximum of the X-ray diffraction rocking curve of the (0002) plane and (10-10) of the AlN crystal film are 100 arcsec or less and 1.7° or less, respectively.
8. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the AlN crystal film is formed by controlling the oxygen content in the AlN crystal film to be 5 atm % or less.
9. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the sapphire substrate has an off-angle of 0.1 to 0.7°.
10. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the sputtering method is an RF sputtering method.
11. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the AlN crystal film is deposited by a sputtering method by placing the sapphire substrate in plasma.
12. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein an AlN crystal film having an oxygen content of 5 atm % or less is formed by forming the AlN crystal film under conditions in which a peak assigned to oxygen is not recognized in gas analysis during plasma discharge.
13. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the sapphire substrate surface is subjected to an N 2 plasma or O 2 plasma treatment and then the AlN single crystal film is deposited on said sapphire substrate surface.
14. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the substrate temperature during deposition of the AlN crystal film on the sapphire substrate surface is from 300 to 800° C.
15. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the thickness of the AlN crystal film is from 10 to 50 nm.
16. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the thickness of the AlN crystal film is from 25 to 35 nm.
17. The method for producing a Group III nitride semiconductor multilayer structure as claimed in claim 1 , wherein the diameter of the sapphire substrate is 100 mm or more.