Low-frequency noise gain and photocurrent gain in quantum well infrared photodetectors

We present a theory of the low-frequency noise gain g_n and photocurrent gain g_p in quantum well infrared photodetectors (QWIPs). Expressions for g_n and g_p in terms of QW capture probability p_c and number of QWs N are obtained. These expressions are valid for any number of QWs N≥1 and capture probability 0≪p_c≤1. The difference of noise gain from photocurrent gain is due to the discrete structure of generation–recombination centers (QWs) in QWIP. The ratio g_n/g_p ranges from 0.5 (for p_c→1) to 1 (for p_c→0). QWIP is well described by a conventional photoconductor theory in the case of low capture probability p_c→1, which corresponds to practical QWIPs. The assumptions of the model are discussed in detail, and a comparison with previously published results is made. © 1999 American Institute of Physics.