Nonlinear response of quantum well infrared photodetectors under low-background and low-temperature conditions

Quantum well IR photodetectors (QWIPs) have been proposed for use in space-based sensing applications. These space systems place stringent performance requirements on IR detectors due to low-irradiance environments and the associated requirement for low-temperature operation. We demonstrate that under these conditions, the responsivity of a QWIP detector depends on frequency and that the shape of the frequency response varies with operational conditions. This nonlinear frequency response is empirically similar to dielectric relaxation effects observed in bulk extrinsic silicon and germanium photoconductors under similar operational conditions. Radiometric characterization data demonstrate how the frequency response varies with temperature, photon irradiance, and bias voltage. These data also show that at tow irradiances and temperatures, the detector response is extremely stow, with response times on the order of seconds. The performance of the QWIP detector is described using standard figures of merit including responsivity, noise, and specific detectivity (D*). We also describe the performance of an IR focal plane array (IRFPA) made with QWIP detectors, under operational conditions that result in long response times. The dependence of this time constant on photon irradiance and operating temperature is also described. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02410-7].