Photoconductivity mechanism of quantum well infrared photodetectors under localized photoexcitation

The physics of photoconductivity of quantum well infrared photodetectors (QWIPs) under nonuniform illumination across QWIP structure (in the direction normal to QWs plane) is studied theoretically with the use of numerical simulation. Local responsivity is a strong function of a coordinate across QWIP; it decreases from emitter to collector, having a constant value in the bulk of QWIP. The mechanism of photoconductivity under localized photoexcitation is related to the formation of the dipole layer (DL), with positive charge located in the photoexcited QW, and negative charge located in a few next QWs towards collector. As a result, electric field outside the DL is increased to cause photocurrent. Parameters of the DL and local responsivity for QWIPs with multiple QWs is calculated using an analytical model. (C) 1998 American Institute of Physics. [S0003-6951(98)04949-3].