GaN-BASED FIELD EFFECT TRANSISTOR

Abstract

A GaN-based field effect transistor (MOSFET) is comprised of a channel layer comprised of p-type GaN, an electron supply layer, a surface layer having band gap energy smaller than that of said electron supply layer, sequentially laminated on a substrate, and recess section is formed by removing a part of the drift layer, the electron supply layer, and the surface layer down to a depth that reaches to the channel layer. A source electrode and a drain electrode are formed so that the recess section positions between them, a gate insulation film is formed on the surface layer and on inner-surface of the recess section including the channel layer, and a gate electrode is formed on the gate insulating film in the recess section.

1 . A GaN-based field effect transistor, comprising:
 a substrate;   a channel layer comprised of p-type or undoped GaN-based compound semiconductor material formed on the substrate;   an electron supply layer formed on the channel layer and comprised of GaN-based compound semiconductor material, the electron supply layer having bandgap energy greater than that of the channel layer;   a surface layer formed on the electron supply layer and comprised of GaN-based compound semiconductor material, the surface layer having bandgap energy smaller than that of the electron supply layer;   a first recess section having a surface of the channel layer as a bottom surface, exposed by removing a part of the surface layer and the electron supply layer;   an insulating film formed on the surface layer and an inner surface of the first recess section;   a gate electrode formed on the insulating film in the first recess section; and   a source electrode and a drain electrode electrically connected to the channel layer, the source electrode and the drain electrode being formed on respective sides of the gate electrode, on a surface of the electron supply layer in a second recess section and a third recess section respectively formed in the surface layer and on a same level.   
     
     
         2 . (canceled) 
     
     
         3 . The GaN-based field effect transistor according to  claim 1 , wherein the surface layer is an n-type or undoped GaN layer. 
     
     
         4 . The GaN-based field effect transistor according to  claim 1 , wherein the surface layer is an Al x Ga 1-x N layer, and
 the electron supply layer is an Al y Ga 1-y N (layer, where x<y.   
     
     
         5 . The GaN-based field effect transistor according to  claim 3 , wherein
 the electron supply layer is an Al z Ga 1-z N layer, where 0≦z< 1 , in which composition ratio z for Al component decreases as approaching to its top surface, so that an uppermost surface of the electron supply layer is comprised of the surface layer comprising the n-type or undoped GaN.   
     
     
         6 . The GaN-based field effect transistor according to  claim 1 , wherein
 the surface layer has a thickness of around 20 nm.   
     
     
         7 . The GaN-based field effect transistor according to  claim 1 , wherein
 the surface layer separates the electron supply layer from the insulating film.   
     
     
         8 . The GaN-based field effect transistor according to  claim 7 , further comprising
 a drift layer between the electron supply layer and the channel layer, comprising p-type or undoped GaN-based compound semiconductor material, the drift layer having bandgap energy smaller than that of the electron supply layer and an impurity concentration lower than that of the channel layer.   
     
     
         9 . The GaN-based field effect transistor according to  claim 7 , wherein
 the surface layer is an n-type or undoped GaN layer.   
     
     
         10 . The GaN-based field effect transistor according to  claim 7 , wherein the surface layer is an Al x Ga 1-x N layer, and
 the electron supply layer is an Al y Ga 1-y N, where x<y.   
     
     
         11 . The GaN-based field effect transistor according to  claim 9 , wherein
 the electron supply layer is an Al z Ga 1-z N layer, where 0≦z<1, in which composition ratio z for Al component decreases as approaching to its top surface, so that an uppermost surface of the electron supply layer is comprised of the surface layer comprising the n-type or undoped GaN.   
     
     
         12 . The GaN-based field effect transistor according to  claim 7 , wherein the surface layer has a thickness of around 20 nm. 
     
     
         13 . A GaN-based field effect transistor, comprising:
 a substrate;   a channel layer comprised of p-type or undoped GaN-based compound semiconductor material formed on the substrate;   an electron supply layer formed on the channel layer and comprised of GaN-based compound semiconductor material, the electron supply layer having bandgap energy greater than that of the channel layer;   a surface layer formed on the electron supply layer and comprised of GaN-based compound semiconductor material, the surface layer having bandgap energy smaller than that of the electron supply layer;   a first recess section having a surface of the channel layer as a bottom surface, exposed by removing a part of the surface layer and the electron supply layer;   an insulating film formed on the surface layer and an inner surface of the first recess section;   a gate electrode formed on the insulating film in the first recess section; and   a source electrode and a drain electrode electrically connected to the channel layer, the source electrode and the drain electrode being formed on respective sides of the gate electrode and on a surface of the electron supply layer in a second recess section and a third recess section respectively formed in the surface layer.   
     
     
         14 . A GaN-based field effect transistor, comprising:
 a substrate;   a channel layer comprised of p-type or undoped GaN-based compound semiconductor material formed on the substrate;   an electron supply layer formed on the channel layer and comprised of GaN-based compound semiconductor material, the electron supply layer having bandgap energy greater than that of the channel layer;   a surface layer formed on the surface of the electron supply layer and comprised of GaN-based compound semiconductor material, the surface layer having bandgap energy smaller than that of the electron supply layer;   a recess section having a surface of the channel layer as a bottom surface, exposed by removing a part of the surface layer and the electron supply layer;   an insulating film formed on the surface layer and an inner surface of the recess section;   a gate electrode formed on the insulating film in the recess section; and   a source electrode and a drain electrode electrically connected to the channel layer, the source electrode and the drain electrode being formed on respective sides of the gate electrode and on a surface of the surface layer,   wherein the surface layer sandwiched between the source electrode or the drain electrode and the electron supply layer is an n-type or undoped GaN layer.