Detailed investigation of electron transport, capture and gain in Al0.3Ga0.7As/GaAs quantum well infrared photodetectors

Abstract

We present an investigation of Al0.3Ga0.7As/GaAs quantum well infrared photodetectors (QWIPs) through detailed ensemble Monte Carlo simulations. Both two-dimensional and three-dimensional electrons are simulated with realistically evaluated scattering rates. Transport of the excited electrons is accurately modelled including the reflections from well–barrier interfaces. The details incorporated into the simulator clarified some important phenomena, as well as verifying the previous predictions. Under large bias, well accumulation occurs non-uniformly, being highest near the emitter. Contrary to previous assumptions, the L valley is found to be the origin of a significant portion of the captured electrons even under typical bias voltages. Γ–L transfer, while decreasing carrier mobility, also increases capture probability and decreases the electron lifetime, having a twofold effect on device gain. The above findings explain the large difference between the gains of AlxGa1−xAs/GaAs (with x ∼ 0.3) and InP/In0.53Ga0.47As (or GaAs/InxGa1−xAs) QWIPs, as well as the bias dependence of gain. The average barrier electron velocity is close to the saturated electron velocity in bulk Al0.3Ga0.7As under moderate and large bias; however, low-field mobility is significantly lower than that in bulk material. While complementing previous work, our results offer a deeper understanding of some important QWIP characteristics by resolving the details of transport and electron dynamics in the device.