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

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 NH 3 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.

1 - 11 . (canceled)  
     
     
         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 NH 3  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 H 2  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  claim 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  claim 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 x Ga 1-x N (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 x Ga 1-x 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 x Ga y In 1-x-y N (0≦x≦1, 0≦y≦1, x+y≦1) and laminated on the GaN single-crystal substrate obtained by the method of making GaN single-crystal substrate according to  claim 12.