Patent ID: 7470941

Claim:
A semiconductor layer structure for a GaN/AlGaN heterojunction field effect transistor comprising: a substrate; a nucleation layer formed on the substrate, the nucleation layer formed of AlN; a buffer layer formed on the nucleation layer, the buffer layer comprised of a material selected from a group consisting of GaN and AlGaN; a channel layer formed on the buffer layer, the channel layer comprised of a material selected from a group consisting of GaN and InGaN; an Schottky barrier layer structure formed on the channel layer, the Schottky layer structure comprising: an undoped Schottky layer comprised of a material selected from a group consisting of AlGaN and InAlGaN; a contact layer structure formed on the Schottky barrier structure, the contact layer structure comprising: a first contact layer formed on the undoped Schottky barrier layer, the first contact layer formed of a compound of materials selected from a group consisting of AlGaN and InAlGaN; and a doped contact cap layer formed on the first contact layer, the doped contact layer formed of a compound of materials selected from a group consisting of GaN and InGaN; wherein the doped contact cap layer is n-doped to approximately between 1×10 19 cm −3 and 7×10 19 cm −3 ; wherein the doped contact cap layer has a thickness approximately between 100 to 600 Å; wherein the doped contact cap layer is formed of In x Ga 1-x N, where x is approximately between 0.0 and 0.1; wherein the first contact layer is n-doped to approximately between 1×10 19 cm −3 and 7×10 19 cm −3 ; wherein the first contact layer has a thickness approximately between 50 to 300 Å; wherein the first contact layer is formed of In x Al y Ga 1-x-y N, where x is approximately between 0.0 and 0.1 and y is approximately between 0.0 and 0.5; wherein the undoped Schottky layer has a thickness approximately between 100 to 300 Å; wherein the substrate is formed of a material selected from a group consisting of SiC, sapphire, GaN, and AlN; and wherein the Schottky layer structure further comprises, between the undoped Schottky layer and the channel layer, a doped Schottky layer and a spacer Schottky layer, with the doped Schottky layer adjacent the undoped Schottky layer and the spacer Schottky layer formed between the doped Schottky layer and the channel layer.