Importance of impurity diffusion for early stage degradation in AlGaN/GaN high electron mobility transistors upon electrical stress

Early stage degradation of AlGaN/GaN high electron mobility transistors (HEMTs) submitted to off- and on-state voltage bias stress was studied using UV light-assisted drain current trapping characteristics. Besides electronic traps generated underneath the gate during off-state stress, both stress conditions lead to trap generation in the transistor access region close to the drain side of the gate edge. UV light-assisted trapping analysis strongly indicates these traps to be located in the AlGaN subsurface layer of the AlGaN/GaN HEMT. Trap evolution during off-state stress performed at base plate temperatures from room temperature to 150 °C was found to exhibit an activation energy of 0.26 eV, consistent with impurity diffusion along dislocations.