Group III-V nitride-based semiconductor substrate, group III-V nitride-based device and method of fabricating the same

Abstract

A group III-V nitride-based semiconductor substrate has: a first layer made of GaN single crystal; and a second layer formed on the first layer, the second layer made of group III-V nitride-based semiconductor single crystal represented by Al x Ga 1-x N, where 0.9<x≦1, wherein a top surface and a back surface of the substrate are flattened.

1 . A group III-V nitride-based semiconductor substrate, comprising:
 a first layer comprising GaN single crystal; and   a second layer formed on the first layer, the second layer comprising group III-V nitride-based semiconductor single crystal represented by Al x Ga 1-x N, where 0.9<x≦1,   wherein a top surface and a back surface of the substrate are flattened.   
   
   
       2 . The group III-V nitride-based semiconductor substrate according to  claim 1 , further comprising:
 a transition layer formed between the first layer and the second layer, the transition layer comprising a composition that changes continuously from GaN to Al x Ga 1-x N, where 0.9<x≦1.   
   
   
       3 . The group III-V nitride-based semiconductor substrate according to  claim 1 , wherein:
 the substrate is in circular form with a diameter of 50 mm or more and a thickness of 200 μm or more.   
   
   
       4 . The group III-V nitride-based semiconductor substrate according to  claim 1 , wherein:
 the substrate comprises a dislocation density of 1×10 8  cm −2  or less on its surface.   
   
   
       5 . The group III-V nitride-based semiconductor substrate according to  claim 1 , wherein:
 the second layer comprises a thickness of 50 μm or more.   
   
   
       6 . The group III-V nitride-based semiconductor substrate according to  claim 1 , wherein:
 the substrate comprises a self-standing substrate.   
   
   
       7 . A group III-V nitride-based device, comprising:
 a layer comprising a group III-V nitride-based semiconductor single crystal represented by Al x Ga 1-x N, where 0.9<x≦1, the crystal comprising a dislocation density of 1×10 8  cm −2  or less; and   a device structure formed on the layer,   wherein the device structure comprises a group III-V nitride-based semiconductor single crystal represented by In y Ga z Al 1-y-z N, where 0≦y≦1, 0≦z≦1 and 0≦y+z≦1.   
   
   
       8 . A method of making a group III-V nitride-based semiconductor substrate, comprising the steps of:
 growing a group III-V nitride-based semiconductor film on a hetero-substrate and then depositing a metal film thereon;   heating the hetero-substrate with the metal film in an atmosphere containing hydrogen gas or hydride gas to form a void in the group III-V nitride-based semiconductor film;   growing a first layer comprising a GaN single crystal thereon;   further growing thereon a second layer comprising a group III-V nitride-based semiconductor single crystal represented by Al x Ga 1-x N, where 0.9<x≦1;   removing the hetero-substrate while leaving the first layer and the second layer to provide the group III-V nitride-based semiconductor substrate; and   flattening a top surface and a back surface of the substrate.   
   
   
       9 . The method according to  claim 8 , wherein:
 the first layer and the second layer are continuously grown in a same reactor.   
   
   
       10 . The method according to  claim 8 , wherein:
 the first layer and the second layer are grown by HVPE.   
   
   
       11 . A method of making a group III-V nitride-based device, comprising the steps of:
 forming a device structure comprising an epitaxial growth layer on the group III-V nitride-based semiconductor substrate as defined in  claim 1 ; and   flattening a back surface of the substrate to remove the first layer to render the second layer exposed,   wherein the group III-V nitride-based device is formed such that the device structure is formed on the second layer.