Investigating the effect of off-state stress on trap densities in AlGaN/GaN high electron mobility transistors

The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300–493 K and 493–573 K, respectively. The trap density at the lower temperature range almost doubled from 1.64 × 1012 to 3.3 × 1012/cm2–eV after a critical voltage for degradation of HEMTs was reached during the off-state drain voltage step-stress. The trap density at the higher temperature range only slightly increased from 8.1 × 1012 and 9.2× 1012/cm2–eV after the device stress. The trap densities were also strongly dependent on drain bias voltage; measurements conducted at higher drain bias voltages exhibited larger trap density due to more hot electrons generated at these conditions.