Generalized relationship between gain, noise, and capture probability of quantum well infrared photodetectors

We show that due to the discrete nature of multiple quantum well structures, the decay function of an energetic electron depends on the spatial extent of the electron wave function. As a result, the current gain of a quantum well infrared photodetector (QWIP) cannot be uniquely specified by the single well capture probability pc. Specifically, for a given pc the current gain of an extended state electron is found to be larger than that of a localized electron. Consequently, for a typical QWIP, it is possible that the photocurrent gain is larger than the dark current gain, resulting in a reduction of dark current induced generation-recombination noise from its expected value.