Photocurrent noise in QWIPs: experiment and theory

The power spectral density of photocurrent noise in QWIP is calculated using the Langevin-transport equation for the electrons in the continuum state. A discrete distribution of the electric field in the active region, instead of the homogeneous one valid for bulk photodetectors, has been used. The analytical results have been compared with experimental data obtained in Quantum Well Infrared Photodetectors (QWIPs) having identical growth sequence, layer width and composition, but different number of wells. The model is able to reproduce the characteristic behavior of the power spectral density, related to the discrete structure of the device, arising as a consequence of the imbalance between the current injected at the emitter and the stream of photoelectrons drifting through the structure.