Investigation of surface charges and traps in gallium nitride/aluminium gallium nitride/gallium nitride high‐voltage transistors via measurements and technology computer‐aided design simulations of transfer characteristics of metal–insulator–semiconductor field‐effect transistors and high‐electron‐mobility transistors

Abstract

This study presents a detailed analysis of the Plasma-enhanced chemical vapour deposition (PECVD) silicon-nitride/semiconductor interface of gallium nitride (GaN) transistors through the study of the transfer characteristics of a large-gate-area metal-insulator-semiconductor field-effect transistor (MISFET). Id –Vg measurements were performed on several MISFETs across the wafer and for all of them the authors observed strong hysteresis between forward and reverse sweeps and a double kink. These features indicate the presence of traps beneath the gate electrode. Neither the hysteresis nor the kinks were seen in the measured high-electron-mobility transistor (HEMT) characteristics suggesting that the passivation/semiconductor interface is electrically responsible for them. The transfer characteristics of the MISFET have been reproduced using a technology computer-aided design (TCAD) deck that includes fixed charges and donor traps at the passivation/semiconductor interface. The impact of these charges on the Id –Vg and their influence on the formation of a surface-inversion layer is here explained through extensive TCAD simulations. This study has also been extended to different temperatures between 35 and 75°C to investigate the change in the transfer characteristics at elevated temperatures. It is shown that the hysteresis observed between forward and reverse sweeps and the transconductance decrease significantly with increasing temperature.