Semiconductor Device

Abstract

A semiconductor device and a method of making the same. The device includes a semiconductor substrate having an AlGaN layer on a GaN layer. The device also includes first contact and a second contact. The average thickness of the AlGaN layer varies between the first contact and the second contact, for modulating the density of an electron gas in the GaN layer between the first contact and the second contact.

1 . A semiconductor device comprising:
 a semiconductor substrate including an AlGaN layer on a GaN layer;   a first contact, and   a second contact,   wherein the average thickness of the AlGaN layer varies between the first contact and the second contact, for modulating the density of an electron gas in the GaN layer between the first contact and the second contact.   
     
     
         2 . The device of  claim 1 , wherein at least part of an upper surface of the AlGaN layer includes a plurality of recesses for varying an average thickness of the AlGaN layer. 
     
     
         3 . The device of  claim 2 , wherein a density of the recesses varies for varying the average thickness of the AlGaN layer. 
     
     
         4 . The device of  claim 2 , wherein the depth of the recesses is between 30% and 100% of the local thickness of the AlGaN layer. 
     
     
         5 . The device of  claim 2 , wherein the recesses are arranged in a regular array. 
     
     
         6 . The device of  claim 2 , wherein the recesses comprise grooves. 
     
     
         7 . The device of  claim 1 , wherein the average thickness T of the AlGaN layer between the first contact and the second contact is in the range 10 nm<T<40 nm. 
     
     
         8 . The device of  claim 1  comprising a High Electron Mobility Transistor (HEMT) having a source, a gate and a drain, wherein the first contact comprises said source, and wherein the second contact comprises said drain. 
     
     
         9 . The device of  claim 8 , wherein the AlGaN layer has a larger average thickness between the source and the gate than between the gate and the drain. 
     
     
         10 . The device of  claim 8 , wherein the average thickness of the AlGaN layer increases from the gate to the drain. 
     
     
         11 . The device of  claim 10 , wherein the average thickness of the AlGaN layer increases either linearly or in a series of one or more steps from the gate to the drain. 
     
     
         12 . The device of  claim 1 , wherein the first contact comprises the anode of a Schottky barrier diode, and wherein the second contact comprises the cathode of said Schottky barrier diode. 
     
     
         13 . The device of  claim 12 , wherein the average thickness of the AlGaN layer increases from the anode to the cathode. 
     
     
         14 . The device of  claim 13 , wherein the average thickness of the AlGaN layer increases either linearly or in a series of one or more steps from the anode to the cathode. 
     
     
         15 . A method of making a semiconductor device, the method comprising:
 forming an GaN layer on a substrate;   forming an AlGaN layer on the GaN layer;   forming a first contact and a second contact of the device; and varying the average thickness of the AlGaN layer between the first contact and the second contact, for modulating the density of an electron gas in the GaN layer between the first contact and the second contact.