LARGE PHOTOCONDUCTIVE GAIN IN QUANTUM-WELL INFRARED PHOTODETECTORS

We demonstrate for the first time that a quantum well infrared photodetector based on bound-to-continuum state intersubband transitions can have a photoconductive gain much greater than unity similar to extrinsic photoconductors. An optical gain g=8.1 was determined by comparing the optical absorption, responsivity, and noise characteristics of two multiquantum well detectors which were identical in every respect except for having a different number of periods (2 and 20). The results suggest that since the photocarrier lifetime τL is not transit time limited, detector optimization to increase τL or optical coupling can be expected to lead to an improved detectivity D*.