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 greater than or equal to 1 and capture probability 0 < p(c) less than or equal to 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. (C) 1999 American Institute of Physics. [S0021-8979(99)06423-3].