Noise gain and detectivity of n-type GaAs/AlAs/AlGaAs quantum well infrared photodetectors

We have investigated noise currents in GaAs/AlAs/AlGaAs quantum well infrared photodetectors (QWIPs). The specific design of these detectors implies a carrier mean-free path of exactly one period of the superlattice with N=20 periods, leading to a carrier capture probability pc≈1 associated with a noise gain gn=1/N at sufficiently small applied bias voltages. The gain values obtained from our measurements are analyzed using three different noise gain models, which predict different dependencies of the detectivity on the capture probability. Our results indicate that a photoconductive QWIP with pc≈1 should have a higher detectivity than a conventional GaAs/AlGaAs QWIP.