Semiconductor device and method of manufacturing the same

Abstract

A semiconductor device according to an embodiment includes a first GaN based semiconductor layer of a first conductive type, a second GaN based semiconductor layer of the first conductive type provided above the first GaN based semiconductor layer, a third GaN based semiconductor layer of a second conductive type provided above a part of the second GaN based semiconductor layer, a epitaxially grown fourth GaN based semiconductor layer of the first conductive type provided above the third GaN based semiconductor layer, a gate insulating film provided on the second, third, and fourth GaN based semiconductor layer, a gate electrode provided on the gate insulating film, a first electrode provided on the fourth GaN based semiconductor layer, a second electrode provided at the side of the first GaN based semiconductor layer opposite to the second GaN based semiconductor layer, and a third electrode provided on the second GaN based semiconductor layer.

What is claimed is: 
     
         1 . A semiconductor device comprising:
 a first GaN based semiconductor layer of a first conductive type;   a second GaN based semiconductor layer of the first conductive type provided above the first GaN based semiconductor layer, the second GaN based semiconductor layer having an impurity concentration of the first conductive type lower than that of the first GaN based semiconductor layer;   a third GaN based semiconductor layer of a second conductive type provided above a part of the second GaN based semiconductor layer;   a fourth GaN based semiconductor layer of the first conductive type provided above the third GaN based semiconductor layer, the fourth GaN based semiconductor layer being an epitaxial growth layer, the fourth GaN based semiconductor layer having the impurity concentration of the first conductive type higher than that of the second GaN based semiconductor layer;   a gate insulating film provided on the second GaN based semiconductor layer, the third GaN based semiconductor layer, and the fourth GaN based semiconductor layer;   a gate electrode provided on the gate insulating film;   a first electrode provided on the fourth GaN based semiconductor layer;   a second electrode provided at the side of the first GaN based semiconductor layer opposite to the second GaN based semiconductor layer; and   a third electrode provided on the second GaN based semiconductor layer.   
     
     
         2 . The device according to  claim 1 , further comprising:
 a plurality of fifth GaN based semiconductor layers of the second conductive type provided above a part of the second GaN based semiconductor layer, the plurality of fifth GaN based semiconductor layers surrounding the first electrode or the third electrode, the plurality of fifth GaN based semiconductor layers being provided to be separated from each other, the plurality of fifth GaN based semiconductor layers having substantially the same impurity concentration of the second conductive type as the third GaN based semiconductor layer.   
     
     
         3 . The device according to  claim 2 , further comprising:
 a sixth GaN based semiconductor layer of the second conductive type provided above a part of the second GaN based semiconductor layer, the sixth GaN based semiconductor layer being in contact with the third electrode, the sixth GaN based semiconductor layer having substantially the same impurity concentration of the second conductive type as the third GaN based semiconductor layer.   
     
     
         4 . The device according to  claim 1 , wherein the first electrode is provided in a groove, one end of the groove being positioned at the fourth GaN based semiconductor layer and the other end is positioned at the third GaN based semiconductor layer, the first electrode being in contact with the third GaN based semiconductor layer. 
     
     
         5 . The device according to  claim 1 , wherein the thickness of the second GaN based semiconductor layer is 1 μm to 20 μm and the impurity concentration of the first conductive type of the second GaN based semiconductor layer is 1×10 16  cm −3  to 2×10 17  cm −3 . 
     
     
         6 . The device according to  claim 1 , wherein the thickness of the third GaN based semiconductor layer is 0.1 μm to 2 μm. 
     
     
         7 . The device according to  claim 3 , wherein the impurity concentrations of the second conductive type of the third GaN based semiconductor layer, the fifth GaN based semiconductor layer, and the sixth GaN based semiconductor layer are higher than the impurity concentration of the first conductive type of the second GaN based semiconductor layer by one digit or more. 
     
     
         8 . The device according to  claim 1 , wherein the first electrode and the third electrode are made of different materials. 
     
     
         9 . The device according to  claim 1 , wherein the second GaN based semiconductor layer and the third electrode are Schottky-connected to each other. 
     
     
         10 . The device according to  claim 1 , wherein the fourth GaN based semiconductor layer and the first electrode and the first GaN based semiconductor layer and the second electrode are ohmic-connected to each other. 
     
     
         11 . A method of manufacturing a semiconductor device, comprising:
 forming a second GaN based semiconductor layer of a first conductive type having an impurity concentration of the first conductive type lower than that of a first GaN based semiconductor layer on the first GaN based semiconductor layer by an epitaxial growth method;   forming a third GaN based semiconductor layer of a second conductive type on the second GaN based semiconductor layer by an epitaxial growth method;   forming a fourth GaN based semiconductor layer of the first conductive type having the impurity concentration of the first conductive type higher than that of the second GaN based semiconductor layer on the third GaN based semiconductor layer by an epitaxial growth method;   etching a part of the fourth GaN based semiconductor layer and the third GaN based semiconductor layer to expose a part of the second GaN based semiconductor layer to form a plurality of first convex portions having a stacked structure of the third GaN based semiconductor layer and the fourth GaN based semiconductor layer;   forming a gate insulating film on the second GaN based semiconductor layer, the third GaN based semiconductor layer, and the fourth GaN based semiconductor layer;   forming a gate electrode on the gate insulating film;   forming a first electrode on the fourth GaN based semiconductor layer;   forming a second electrode at the side of the first GaN based semiconductor layer opposite to the second GaN based semiconductor layer; and   forming a third electrode on the second GaN based semiconductor layer.   
     
     
         12 . The method according to  claim 11 , further comprising:
 etching a part of the fourth GaN based semiconductor layer and the third GaN based semiconductor layer to form a plurality of second convex portions of the third GaN based semiconductor layer being separated from each other.   
     
     
         13 . The method according to  claim 12 , further comprising:
 etching a part of the third GaN based semiconductor layer of the second convex portions to expose the second GaN based semiconductor layer for forming the third electrode.   
     
     
         14 . A method of manufacturing a semiconductor device, comprising:
 forming a second GaN based semiconductor layer of a first conductive type having an impurity concentration of the first conductive type lower than that of a first GaN based semiconductor layer on the first GaN based semiconductor layer by an epitaxial growth method;   covering a part of the second GaN based semiconductor layer by a first mask material   forming a third GaN based semiconductor layer of a second conductive type by a selective epitaxial growth method on the second GaN based semiconductor layer;   forming a fourth GaN based semiconductor layer of the first conductive type having the impurity concentration of the first conductive type higher than that of the second GaN based semiconductor layer on at least a part of the third GaN based semiconductor layer by a selective epitaxial growth method;   forming a gate insulating film on the second GaN based semiconductor layer, the third GaN based semiconductor layer, and the fourth GaN based semiconductor layer;   forming a gate electrode on the gate insulating film;   forming a first electrode on the fourth GaN based semiconductor layer;   forming a second electrode at the side of the first GaN based semiconductor layer opposite to the second GaN based semiconductor layer; and   forming a third electrode on the second GaN based semiconductor layer.   
     
     
         15 . The method according to  claim 14 , wherein a part of the third GaN based semiconductor layer is covered by a second mask material, when forming the fourth GaN based semiconductor layer.