Current noise in quantum well infrared photodetectors: effect of electron Coulomb interaction

The power spectrum of current noise in quantum well infrared photodetectors (QWIPs) is calculated, considering the smoothing effect of long-range Coul omb interaction on the noise in order to account for the shot-noise suppres sion observed in QWIPs at low external biases. When the external voltage is low, the random emission of each electron from the cathode, due to the pot ential distribution through the device, reduces the transmission probabilit y of the triangular emitter barrier during its transit time, giving a feedb ack effect on the current fluctuations. From a statistical point of view, i n each interaction volume the time interval between two consecutive electro n injections cannot be therefore described by Poisson statistics, which are valid for fully independent electrons. The work will be thus addressed to deducing a statistics accounting for the correlation between electrons duri ng their transit through the device. Finally, it will be shown that at low frequencies the power spectral density of noise, calculated using such stat istics, is reduced by a factor of up to 0.5, depending on the operating con ditions of the device.