Abstract

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.

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