A Novel Transparent AZO-Gated $\hbox {Al}_{0.2} \hbox {Ga}_{0.8}\hbox {As/In}_{0.2}\hbox {Ga}_{0.8}\hbox {As}$ pHEMT and Photosensing Characteristics Thereof

A novel transparent Al-doped ZnO (AZO)-gated Al_0.2Ga_0.8As/In_0.2Ga_0.8As pseudomorphic high-electron mobility transistor (pHEMT) has been comprehensively investigated. The proposed AZO-gated pHEMT has demonstrated superior temperature-dependent performance, including two-terminal gate-drain breakdown/turn-on voltages of - 63/3.4 (-56.4/3.4) V, an intrinsic voltage gain A_V of 257 (176), and a gate voltage swing of 1.18 (1.13) V at 300 (450) K. An excellent thermal threshold coefficient ∂V_th/ΘT of -1.8 mV/K was also obtained. A conventional Au-gated device with the same gate dimensions of 1 × 100 μm² was also fabricated in comparison. In addition, high optical transmittance values of 82%-98% for incident energy values of 1.24-3.54 eV are achieved in the AZO film. The present AZO-gated HEMT has demonstrated three-terminal tunable optical responsivity due to a photovoltaic effect. Photosensing characteristics under different radiation wavelengths of white light, red light (632 nm), and near infrared (980 nm) are also studied.