Langevin approach to the generation-recombination noise of a multi quantum well infrared photodetector

The current noise power spectrum of a multi quantum well infrared photodetector is calculated using a Langevin-transport equation where a discrete distribution of the electric field in the quantum well region, rather than the homogeneous one valid for bulk semiconductors, has been considered. The discreteness of the electric field arises as a consequence of the discrete structure of the quantum well layers. The inhomogeneous charge distribution in the quantum well structure affects the intensity and the frequency dependence of the noise power spectrum, giving rise to deviations from the behavior expected on the basis of a simple model based on fully uncorrelated fluctuation processes. The model reproduces the different N-dependence of the current noise power spectral density in the dark and in the presence of radiation. In particular, its relation to the discrete structure of the device arises as a consequence of the imbalance between the current injected at the emitter and the stream of photoelectrons drifting through the structure, whose effect seems particularly relevant for small values of the number of quantum wells N.