Gain and recombination dynamics of quantum-dot infrared photodetectors

The high photoconductive gain observed in semiconductor quantum dot infrared detectors (QDIPs) constitutes one of the most exciting recent topics in nanotechnology. In this paper we present a theory of diffusion and recombination in QDIPs which is an attempt to explain the recently reported values of gain in these devices. We allow the kinetics to encompass both the diffusion and capture rate limited regimes of carrier relaxation using rigorous random walk and diffusion methods. The photoconductive gains are calculated and compared with the experimental values obtained from InGaAs∕InGaP∕GaAs and InAs∕InP QDIPs using the generation-recombination noise analysis. It is found that the gain can indeed exhibit a broad range of values, including up to several thousands, depending on the bias and the type of material investigated. We also predict the photocurrent transients, and relate them to recent experiments using terahertz pulse spectroscopy.