Time-dependent effects in QWIPs in low temperature, low background conditions

Abstract

Recently, several time-dependent effects have been observed in both the dark current and the photocurrent of quantum well infrared photodetectors (QWIPs) when operating in a low temperature and/or low photon background. These effects include: non-zero dark current when the applied bias is zero, hysteresis in the dark current when the applied bias is varied, chaotic oscillations in the dark current at high applied bias, a linear increase in the dark current when the frequency of a sinusoidal applied bias is increased, and a roll-off in the optical responsivity when the frequency of a time-varying photo signal is increased. In this paper, we explain how these effects are all manifestations of a single property: QWIPs behave like an RC circuit, with a resistance in series with the capacitance. Here we show the microscopic origin of both the transport resistance (due to tunneling in the dark cases, and due to photoexcitation when a photo signal is applied) and the quantum well capacitance. We also show that the non-adiabatic field that arises due to the capacitive time constant enters the theory non-linearly, leading to the oscillations at high bias first predicted and then observed.