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 - 20 . (canceled) 
     
     
         21 . A method of making a nitride type semiconductor epitaxial substrate, the method comprising steps 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 a NH 3  gas and a H 2  gas, said surface of said GaN single-crystal substrate having a root-mean-square roughness of 0.2 nm or less; and   epitaxially growing a nitride compound semiconductor layer, on said GaN single-crystal substrate, said GaN single-crystal substrate being obtained without oxidizing said surface of said GaN single-crystal substrate, and said nitride compound semiconductor layer having a surface with a root-mean-square roughness of 0.2 nm or less,   wherein both said epitaxial growth and said heat treatment of said GaN single-crystal substrate are effected within a reactor for carrying out said epitaxial growth,   the nitride compound is of the general formula Al x In y Ga 1-x-y N, and   0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1.   
     
     
         22 . The method according to  claim 21 , wherein said surface of said GaN single-crystal substrate is mechanical polished. 
     
     
         23 . The method according to  claim 21 , said method comprising the step of:
 carrying out mechanical polishing of a GaN single-crystal article to form the polished surface of the GaN single-crystal.   
     
     
         24 . The method according to  claim 23 , wherein the root-mean-square roughness of the heat-treated surface is smaller than that of the mechanical polished surface. 
     
     
         25 . The method according to  claim 21 , wherein said nitride compound semiconductor layer has an x-ray diffraction half width of 100 seconds or less. 
     
     
         26 . The method according to  claim 21 , wherein said nitride compound semiconductor layer has a threading dislocation density of 1×10 6  cm −2  or less. 
     
     
         27 . The method according to  claim 22 , wherein a plurality of defects are formed in said GaN single crystal substrate by mechanical polishing such that the substrate surface, after mechanical polishing, has an Rms (root-mean-square roughness) of about 1.0 nm.