Distribution of trap energy level in AlGaN/GaN high-electron-mobility transistors on Si under ON-state stress

The distribution of trap energy (DTE) levels was observed in the energy band gap of buffer GaN by temperature-dependent current transient measurements on AlGaN/GaN HEMTs under fully ON drain-stress (VD[ON]_Stress) conditions. The activation energies (Ea's) obtained from current transients increase with increasing VD[ON]_Stress. Using a multitrap energy (MTE) model, the applied-VD[ON]_Stress-dependent Ea is attributed to DTE levels in the GaN energy band gap, rather than to discrete single trap energy levels. An effective activation energy (Ea_eff) corresponding to trap energy levels activated by the applied VD[ON]_Stress is thus obtained. This observation is validated with two-dimensional numerical simulations. This study will help device designers develop a "DTE-dependent" emission time constant model that is readily applicable for the reliability modelling of future GaN-based circuits.