Anomalous Decrease of Off-State Drain Leakage Current in GaN/AlGaN HEMTs With Dual Optical Excitation

We report an anomalous decrease of off-state drain leakage current (I_Off-state) of GaN/AlGaN HEMTs upon dual optical excitation. The phenomenon was observed accidentally during dc characterization of devices when both fluorescent white room light and incandescent optical microscope light were turned on. A similar phenomenon was observed and verified through simultaneous optical excitation of both ultraviolet (UV ~350 nm) light and 532-nm green light. A spectrally resolved measurement revealed broad trap level centered ~2.27 eV. The decrease of I_Off-state during dual excitation is owing to the optical quenching of photoconductivity in GaN buffer layer. This quenching effect is originated from enhanced light-defect interaction, where sub-band gap light reduces photoconductivity induced by above bandgap light. Observation of this phenomenon would provide us an alternative way to characterize GaN buffer layer quality for the development of GaN HEMTs.