Group iii nitride based semiconductor substrate and process for manufacture thereof

Abstract

To provide a semiconductor substrate of a group III nitride with a little warp, this invention provides a process comprising such steps of: epitaxial-growing a GaN layer 33 with a GaN low temperature grown buffer layer 32 upon a sapphire substrate 31; removing the sapphire substrate 31, the GaN buffer layer 32 and a small portion of the GaN layer 33 from the substrate taken out of a growth reactor to obtain a self-supporting GaN substrate 35; and after that, heat-treating the GaN substrate 35 by putting it into an electric furnace under the NH 3 atmosphere at: 1200° C. for 24 hours; which leads to a marked reduction of the warp of the self-supporting GaN substrate 35 such that dislocation densities of its obverse and reverse surface are 4×10 7 cm −2 and 8×10 5 cm −2 , and thereby such a low ratio of dislocation densities of 50 is well-controlled.

1 . A group III nitride based semiconductor substrate which is a self-supporting substrate; wherein 
 when a dislocation density of a surface thereof on a side of a lower dislocation density is designated n, and a dislocation density of a surface thereof on a side of a higher dislocation density is designated n 2 , its ratio of n 2 /n 1  is less than 750.    
   
   
       2 . A group III nitride based semiconductor substrate claimed in  claim 1 , wherein n, is not higher than 1×10 8  cm −2 .  
   
   
       3 . A group III nitride based semiconductor substrate which is a self-supporting substrate; wherein 
 when an edge dislocation density of a surface thereof on a side of a lower edge dislocation density is designated m 1  and an edge dislocation density of a surface thereof on a side of a higher edge dislocation density is designated m 2 , its ratio of m 2 /m 1  is less than 1000.    
   
   
       4 . A group III nitride based semiconductor substrate claimed in  claim 3 , wherein ml is not higher than 5×10 7  cm −2 .  
   
   
       5 . A group III nitride based semiconductor substrate claimed in any one of claims  1 - 4 , wherein a thickness thereof is not less than 30 μm but not greater than 1 mm.  
   
   
       6 . A group III nitride based semiconductor substrate claimed in any one of claims  1 - 5 , wherein it comprises a layer made of GaN or AlGaN.  
   
   
       7 . A process for manufacturing a group III nitride based semiconductor substrate; which comprises the steps of: 
 forming a group III nitride based semiconductor layer on top of a substrate of a different material;    separating said substrate of the different material from said group III nitride based semiconductor layer; and    applying a treatment to reduce a dislocation density onto a surface of said group III nitride based semiconductor layer which lies on a side from which said substrate of the different material has been separated.    
   
   
       8 . A process for manufacturing a group III nitride based semiconductor substrate; which comprises the step of 
 forming a group III nitride based semiconductor layer on top of a substrate of a different material by epitaxial growth, and thereafter separating said substrate of the different material from said group III nitride based semiconductor layer; wherein    a heat treatment is carried out at a temperature not lower than 1150° C. either during the growth of said group III nitride based semiconductor layer or after the growth of said group III nitride based semiconductor layer.    
   
   
       9 . A process for manufacturing a group III nitride based semiconductor substrate according to  claim 8 , which further comprises the step of applying a treatment to reduce a dislocation density onto a surface of said group III nitride based semiconductor layer which lies on a side from which said substrate of the different material has been separated.  
   
   
       10 . A process for manufacturing a group III nitride based semiconductor substrate according to  claim 7  or  9 , 
 wherein said treatment to reduce a dislocation density comprises the step of removing a region of said group III nitride based semiconductor layer to a thickness not less than 100 Am from a side from which said substrate of the different material has been separated.    
   
   
       11 . A process for manufacturing a group III nitride based semiconductor substrate according to  claim 7 ,  9  or  10 , 
 wherein said treatment to reduce a dislocation density comprises the step of applying a heat treatment onto said group III nitride based semiconductor layer at a temperature not lower than 1150° C.