Evolution of Deep Traps in GaN-Based RF High Electron Mobility Transistors under High Voltage OFF-State Stress

An unrecoverable degradation of gate leakage is observed in AlGaN/GaN high electron mobility transistors (HEMTs) under high OFF-state drain bias stress up to 200 V. Current-mode deep-level transient spectroscopy is developed for in situ observation of evolution of traps in the HEMTs before and after stress. It is revealed that two discrete traps, with activation energy of 0.54 and 0.69 eV, have converted into a deeper and broader trap (0.86 eV) after the stress, along with an increased apparent capture cross section (from 1.71 x 10(-17)-1.11 x 10(-15) cm(2) to 9.05 x 10(-15) cm(2)). The conversion lowers down the tunneling barrier between metal and the AlGaN barrier, which facilitates trap-assisted gate leakage in reversed biased AlGaN/GaN HEMTs. Engineering of deep traps in the AlGaN/GaN epilayers is essential for promoting and upgrading of power capability of GaN-based RF HEMTs.