Design and implementation of bound-to-quasibound GaN/AlGaN photovoltaic quantum well infrared photodetectors operating in the short wavelength infrared range at room temperature

In this paper, we discuss the design of photovoltaic quantum well infrared photodetectors (QWIPs) based on polar GaN/AlGaN multiquantum wells (MQWs). Getting a reasonable escape probability of the excited electron requires adjusting the bound-to-quasibound intersubband transition in the absorbing quantum well and engineering the polarization-related internal electric field in the barriers. This can be achieved with a MQW period that consists of 3 layers, namely, the active quantum well, an extraction barrier, and an injection barrier, the latter being thin enough to allow tunneling transport. Following this design scheme, we demonstrate bound-to-quasibound GaN/AlGaN QWIPs with peak photocurrent response at 2.3 μm, operating at room temperature in both photovoltaic and photoconductive modes. Based on high-resolution x-ray diffraction measurements, the entire detector structure, which included a 40-period MQW with 30 nm-thick barriers, along with top and bottom contact layers of combined thickness above 900 nm, was grown pseudomorphically on an AlGaN-on-sapphire template. A room-temperature responsivity of 88 μA/W was measured at zero bias, increasing up to 302 μA/W at −1.0 V bias. The responsivity reached its maximum at 150–200 K, where it was approximately a factor of 2 higher than at room temperature. Ideas for a new device structure to improve the QWIP response in the photovoltaic mode are proposed.