Current instabilities and other reliability aspects in AlGaN/GaN MOS-HFETs with atomic layer deposited Al2O3 as gate oxide

An impact of the different voltage ramps (from 25mV/s to 20V/s) in off-state regime for HFET and MOS-HFET was experimentally investigated. Because of the temperature in the channel drops at low voltage steps, density of temperature-active interface states and states in the GaN buffer near the channel is reduced, and therefore the I_DS,off-state decreases. A positive temperature coeficient is attended. An another behaviour for MOS-HFET for fast traps in comparison to HFET was observed. A smaller temperature-dependence of fast traps in comparison to slow traps can be responsible for this effect. The same tendency of I_DS,off.state for all devices were found. The MOSHFET exhibited no change of drain current I_DS,off-state for 5 hours, but for the HFET the value was more than 500 times higher.