Gate current leakage and breakdown mechanism in unpassivated AlGaN/GaN high electron mobility transistors by post-gate annealing

Gate leakage/breakdown mechanism in unpassivated AlGaN/GaN high electron mobility transistors (HEMTs) is investigated by performing temperature-dependent pulsed current-voltage (I-V) and current transient measurements of AlGaN/GaN HEMTs without and with annealing after Schottky gate formation. After post-gate annealing, the devices exhibited significantly smaller gate leakage current and higher breakdown voltage even without any gate dielectrics or passivation layer. The temperature-dependent current transient measurements show that the current dispersion in the unannealed HEMTs is attributed to traps with an emission time constant (t(E)) of similar to 0.5 mu s at 295 K and an activation energy of similar to 38 meV. On the contrary, the 20-min annealed devices have traps with t(E) of 21.6 mu s at 295 K and an activation energy of similar to 0.31 eV. The results suggest that the post-gate annealing removes shallow traps, and creates or activates deeper traps. We propose that the breakdown and gate leakage current is mainly due to the emission current from shallow traps in unpassivated AlGaN/GaN HEMTs. The breakdown voltage improvement after the post-gate annealing is due to the removal of shallow traps near the Schottky gate metal/AlGaN interface. (C) 2005 American Institute of Physics.