IMPROVING GAN/ALGAN/GAN HFET TRANSCONDUCTANCE AND GATE LEAKAGE BY REDUCING THE ELECTRON SHEET DENSITY THROUGH HIGH TEMPERATURE ANNEALING

Paper in proceeding, 2010

An LPCVD silicon nitride is used to passivate GaN/AlGaN/GaN heterostructures. The nitride is deposited before the high temperature annealing step that is used to form ohmic contacts. The contact annealing will reduce the electron sheet density of a non-passivated heterostructure, but is seen to have almost no effect on the LPCVD passivated heterostructure. From a first examination the reduction of ns is a negative effect. However, in this report it is shown that introducing an extra annealing step before the LPCVD deposition can be used to improve device characteristics. A pre-LPCVD annealing at 800°C reduces ns by 15%, resulting in: almost no change in sheet resistance, around 40% larger transconductance and a substantially lower gate current.