Crystal film, crystal substrate, and semiconductor device

Abstract

A crystal foundation having dislocations is used to obtain a crystal film of low dislocation density, a crystal substrate, and a semiconductor device. One side of a growth substrate ( 11 ) is provided with a crystal layer ( 13 ) with a buffer layer ( 12 ) in between. The crystal layer ( 13 ) has spaces ( 13 a ), ( 13 b ) in an end of each threading dislocation D 1 elongating from below. The threading dislocation D 1 is separated from the upper layer by the spaces ( 13 a ), ( 13 b ), so that each threading dislocation D 1 is blocked from propagating to the upper layer. When the displacement of the threading dislocation D 1 expressed by Burgers vector is preserved to develop another dislocation, the spaces ( 13 a ), ( 13 b ) vary the direction of its displacement. As a result, the upper layer above the spaces ( 13 a ), ( 13 b ) turns crystalline with a low dislocation density.

1 . A method of making a crystal film, the method comprising:
 a step of growing a III-V compound semiconductor layer at a first growth rate, said first growth rate differing from a second growth rate;   a step of forming a pit within the III-V compound crystal layer by growing said III-V compound semiconductor layer at said second growth rate, a threading dislocation within the III-V compound semiconductor layer terminating at said pit.   
     
     
         2 . The method of  claim 1 , wherein said threading dislocation extends to an apex of the pit. 
     
     
         3 . The method of  claim 1 , further comprising:
 a step of enclosing the pit within said III-V compound semiconductor layer, a growth rate of the III-V compound crystal layer being changed from said second growth rate to said third growth rate during the step of enclosing the pit.   
     
     
         4 . The method of  claim 3 , wherein said third growth rate differs from said second growth rate. 
     
     
         5 . The method of  claim 3 , wherein said third growth rate is said first growth rate. 
     
     
         6 . The method of  claim 3 , wherein a space is formed within the III-V compound crystal layer during the step of enclosing the pit, said space being a void within the III-V compound crystal layer. 
     
     
         7 . The method of  claim 1 , wherein a Group 3B elements source gas is supplied with a Group 5B elements source gas during the step of growing the III-V compound semiconductor layer. 
     
     
         8 . The method of  claim 7 , wherein a ratio of the Group 3B elements source gas to the Group 5B elements source gas is changed during the step of forming the pit. 
     
     
         9 . The method of  claim 7 , wherein a supply of the Group 3B elements source gas is stopped during the step of forming the pit. 
     
     
         10 . The method of  claim 7 , wherein a growth rate of the III-V compound crystal layer during the step of forming the pit is changed from said first growth rate to said second growth rate. 
     
     
         11 . The method of  claim 1 , wherein said threading dislocation propagates into said III-V compound crystal layer from within a buffer layer. 
     
     
         12 . The method of  claim 11 , wherein said buffer layer is between a substrate and said III-V compound crystal layer. 
     
     
         13 . The method of  claim 12 , wherein a difference in thermal expansion coefficients exists between said buffer layer and said substrate. 
     
     
         14 . The method of  claim 12 , wherein said buffer layer is gallium nitride. 
     
     
         15 . The method of  claim 12 , wherein said substrate and said III-V compound crystal layer. 
     
     
         16 . The method of  claim 12 , wherein said substrate is made of a crystalline material. 
     
     
         17 . The method of  claim 12 , wherein said substrate is a material from the group consisting of sapphire, silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs), silicon (Si), a composite oxide of magnesium and aluminum (MgAl 2 O 4 ; spinel), and a composite oxide of lithium and gallium (LiGaO 2 ). 
     
     
         18 . The method of  claim 1 , further comprising:
 a step of forming a coat film on said pit.   
     
     
         19 . The method of  claim 18 , wherein said coat film is an amorphous material. 
     
     
         20 . The method of  claim 18 , wherein said coat film is a metal material. 
     
     
         21 . The method of  claim 18 , wherein said metal material is from the group consisting of aluminum (Al), gallium (Ga), indium (In), magnesium (Mg), zirconium (Zr), and titanium (Ti). 
     
     
         22 . The method of  claim 18 , wherein said coat film includes a material from the group consisting of oxygen, nitrogen, fluorine and carbon. 
     
     
         23 . The method of  claim 18 , wherein said threading dislocation extends to said coat film.