Off-State Drain Leakage Current Mechanism in GaN High Electron Mobility Transistors from Thermal Storage Test

The effect of the thermal storage test on GaN high electron mobility transistor (HEMT) is investigated in this study by observing off-state drain leakage current and on-state hysteresis and maximum transconductance. The recovery post thermal stress is also observed which points to native defects within the heterostructure as the leakage values after 72 hrs of recovery are measured to be one order higher than the pristine device. On-state hysteresis recovery and off-state drain leakage are dominated by similar defects as observed from the characteristic recovery times. Trap analysis through drain current spectroscopy reveals an additional trap level of E-C - 0.83 eV from the thermal storage test. The electrical measurements are in close correlation with the E2H Raman active mode leading to reduced lifetimes (approximate to 0.44 ps) at higher temperatures, where anharmonic phonon decay is observed following the reported Balkanski model. This gives an overall picture of the phonon-induced defect generation from the thermal stress and the recovery from the reduced scattering probability within the material observed after 72 hrs recovery; also observed within the HEMTs from electrical characterization.