Electron transfer in voltage tunable two-color infrared photodetectors

Abstract

Two-color quantum-well infrared photodetectors (QWIPs) that are based on electron transfer between coupled QWs suffer from the presence of the shorter wavelength peak at all bias voltages. We investigate this problem in such detectors with 50 or 200 Å AlGaAs barriers between the QW pair. We deduce the absorption coefficient α and photoconductive gain g of the detectors with 50 Å barriers using corrugated QWIPs with different corrugation periods. We find that α has a number of small peaks in its spectrum but its value remains almost constant between 0.1 and 0.2 μm−1 in the 6–12 μm range for most experimental conditions. The wavelength dependence of g, which always has a pronounced peak at the shorter detection wavelength, determines the responsivity line shape. These results are attributed to insufficient electron transfer between the coupled QWs and to low tunneling probability of the longer wavelength photoelectrons. A comparison of measured responsivity and calculated absorption spectrum of the detectors with 200 Å barriers indicates that there is significant electron transfer between the coupled wells. Despite efficient electron transfer, these detectors have a shorter wavelength detection peak at all bias voltages because of significant short wavelength absorption in both the QWs.