Degradation of sub-micron gate AlGaN/GaN HEMTs due to reverse gate bias

GaN High Electron mobility transistors (HEMTs) were electrically step-stressed under high reverse gate bias conditions. Once a threshold voltage is reached, gate current increases about two orders of magnitude. Though critical voltage was determined to be linear with increasing gate length, electrical simulations show that the maximum electric field was similar at the critical voltage (~2 MV.cm^-1). Electroluminescence and photoluminescence performed on the degraded samples exhibited a decrease in intensity along the periphery of the gate. Transmission electron microscopy shows a thin native oxide layer present under that gate before stressing, and the first stages of gate metal reacting with the underlying AlGaN after stressing.