Investigating the effect of thermal annealing on dc performance of off-state drain-voltage step-stressed AlGaN/GaN high electron mobility transistors

The effects of a thermal annealing process on the dc performance of off-state, drain-voltage step-stressed AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. After stress, the reverse bias gate leakage current increased from 7 × 10^-3 to 1.96 × 10^-1mA/mm and drain current on-off ratio decreased from 1.9 × 10⁵ to 4.52 × 10³. These degradations were completely recovered after a thermal annealing at 450 °C for 10 min. Temperature-dependent drain-current subthreshold swing measurements were employed to estimate the trap densities located in the AlGaN barrier layer near-surface region of the HEMTs before and after off-state drain-voltage step-stressing and also following subsequent thermal annealing. Off-state step-stressing produced a significant increase of trap density from 2.15 × 10¹² to 1.63 × 10¹³/cm² V. This was reduced to 5.21 × 10¹²/cm² V after thermal annealing. These results show that simple thermal annealing can recover much of the degradation caused by step-stressing below the threshold for permanent damage.