Normally off iii nitride transistor

Abstract

A semiconductor device containing an enhancement mode GaN FET on a III-N layer stack includes a low-doped GaN layer, a barrier layer including aluminum over the low-doped GaN layer, a stressor layer including indium over the barrier layer, and a cap layer including aluminum over the stressor layer. A gate recess extends through the cap layer and the stressor layer, but not through the barrier layer. The semiconductor device is formed by forming the barrier layer with a high temperature MOCVD process, forming the stressor layer with a low temperature MOCVD process and forming the cap layer with a low temperature MOCVD process. The gate recess is formed by a two-step etch process including a first etch step to remove the cap layer, and a second etch step to remove the stressor layer.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a buffer layer;   a first III-N material over the buffer layer;   a second III-N material over the first III-N material;   a third III-N material disposed over the second III-N material, the third III-N having less than 1 atomic percent indium;   an indium aluminum nitride layer over the third III-N, the indium aluminum nitride layer having a stoichiometry of In 0.05 Al 0.95 N to In 0.30 Al 0.70 N, and a thickness of 1 nanometer to 5 nanometers;   a cap layer of III-N material disposed over the indium aluminum nitride layer;   a gate recess extending through the cap layer and the indium aluminum nitride layer in an enhancement mode gallium nitride field effect transistor (GaN FET), wherein the gate recess does not extend through the third III-N;   a gate dielectric layer disposed over the third III-N in the gate recess; and   a gate of the enhancement mode GaN FET disposed over the gate dielectric layer in the gate recess.   
     
     
         2 . The semiconductor device of  claim 1 , wherein the third III-N has a stoichiometry of Al 0.10 Ga 0.90 N to Al 0.30 Ga 0.70 N, and a thickness of 1 nanometer to 5 nanometers. 
     
     
         3 . The semiconductor device of  claim 1 , wherein the indium aluminum nitride layer has a stoichiometry of In 0.16 Al 0.84 N to In 0.18 Al 0.82 N and a thickness of 3.5 nanometers to 4.5 nanometers. 
     
     
         4 . The semiconductor device of  claim 1 , wherein the cap layer has a stoichiometry of Al 0.05 Ga 0.95 N to Al 0.30 Ga 0.70 N, and a thickness of 4 nanometers to 20 nanometers. 
     
     
         5 . The semiconductor device of  claim 1 , wherein the gate dielectric layer comprises a material selected from the group consisting of silicon dioxide, silicon nitride, or aluminum oxide. 
     
     
         6 . The semiconductor device of  claim 1 , wherein the gate comprises polysilicon. 
     
     
         7 . A semiconductor device, comprising:
 a buffer layer;   a first GaN layer over the buffer layer;   a second GaN layer over the first GaN layer;   a first AlGaN layer disposed over the second GaN layer, the first AlGaN layer having less than 1 atomic percent indium;   an indium aluminum nitride layer over the AlGaN layer;   a second AlGaN layer disposed over the indium aluminum nitride layer;   a gate recess extending through the second AlGaN layer and the indium aluminum nitride layer in an enhancement mode GaN FET, wherein the gate recess does not extend through the first AlGaN layer;   a gate dielectric layer of the enhancement mode GaN FET disposed over the first AlGaN layer in the gate recess; and   a gate of the enhancement mode GaN FET disposed over the gate dielectric layer in the gate recess.   
     
     
         8 . The semiconductor device of  claim 7 , further comprising:
 a gate dielectric layer of a depletion mode GaN FET disposed over the second AlGaN layer, the indium aluminum nitride layer and the first AlGaN layer; and   a gate of the depletion mode GaN FET disposed over the gate dielectric layer of the depletion mode GaN FET.   
     
     
         9 . The semiconductor device of  claim 8 , wherein:
 the gate dielectric layer of the enhancement mode GaN FET and the gate dielectric layer of the depletion mode GaN FET have substantially equal thicknesses and compositions; and   the gate of the enhancement mode GaN FET and the gate of the depletion mode GaN FET have substantially equal compositions.   
     
     
         10 . The semiconductor device of  claim 9 , wherein the gate dielectric layer of the enhancement mode GaN FET and the gate dielectric layer of the depletion mode GaN FET comprise a material selected from the group consisting of silicon dioxide, silicon nitride, or aluminum oxide. 
     
     
         11 . The semiconductor device of  claim 10 , wherein the gate of the enhancement mode GaN FET and the gate of the depletion mode GaN FET comprise polysilicon. 
     
     
         12 : The semiconductor device of  claim 7 , wherein the first AlGaN layer has a stoichiometry of Al 0.10 Ga 0.90 N to Al 0.30 Ga 0.70 N, and a thickness of 1 nanometer to 5 nanometers. 
     
     
         13 . The semiconductor device of  claim 7 , wherein the indium aluminum nitride layer has a stoichiometry of In 0.16 Al 0.84 N to In 0.18 Al 0.82 N and a thickness of 3.5 nanometers to 4.5 nanometers. 
     
     
         14 . The semiconductor device of  claim 7 , wherein the second AlGaN layer has a stoichiometry of Al 0.05 Ga 0.95 N to Al 0.30 Ga 0.70 N, and a thickness of 4 nanometers to 20 nanometers. 
     
     
         15 . A semiconductor device, comprising:
 a buffer layer;   a first GaN layer over the buffer layer;   a second GaN layer over the first GaN layer;   a first AlGaN layer disposed over the second GaN layer, the first AlGaN layer having less than 1 atomic percent indium;   an indium aluminum nitride layer over the AlGaN layer;   a second AlGaN layer disposed over the indium aluminum nitride layer;   a gate recess extending through the second AlGaN layer and the indium aluminum nitride layer in an enhancement mode GaN FET, wherein the gate recess does not extend through the first AlGaN layer;   a gate dielectric layer of the enhancement mode GaN FET disposed over the first AlGaN layer in the gate recess;   a gate of the enhancement mode GaN FET disposed over the gate dielectric layer in the gate recess;   a gate dielectric layer of a depletion mode GaN FET disposed over the second AlGaN layer, the indium aluminum nitride layer and the first AlGaN layer; and   a gate of the depletion mode GaN FET disposed over the gate dielectric layer of the depletion mode GaN FET.   
     
     
         16 . The semiconductor device of  claim 15 , wherein the first AlGaN layer has a thickness of 1 nanometer to 5 nanometers. 
     
     
         17 . The semiconductor device of  claim 15 , wherein the indium aluminum nitride layer has a thickness of 3.5 nanometers to 4.5 nanometers. 
     
     
         18 : The semiconductor device of  claim 15 , wherein the second AlGaN layer has a thickness of 4 nanometers to 20 nanometers. 
     
     
         19 . The semiconductor device of  claim 15 , wherein:
 the gate dielectric layer of the enhancement mode GaN FET and the gate dielectric layer of the depletion mode GaN FET have substantially equal thicknesses and compositions; and   the gate of the enhancement mode GaN FET and the gate of the depletion mode GaN FET have substantially equal compositions.   
     
     
         20 . The semiconductor device of  claim 15 , wherein the gate dielectric layer of the enhancement mode GaN FET and the gate dielectric layer of the depletion mode GaN FET comprise aluminum oxide.