Towards a voltage tunable two-color quantum-well infrared photodetector

Abstract

Two-color quantum-well infrared photodetectors (QWIPs), based on electron transfer between coupled QWs, suffer from the presence of the shorter wavelength peak at all bias voltages Vb. We investigate this problem by studying the bias dependence of absorption coefficient α and photoconductive gain g as a function of wavelength at 10 K. We fabricate such a detector with a peak wavelength of 8 μm for both bias polarities but a voltage tunable cutoff wavelength (9 μm for Vb>0 and 11 μm for Vb<0). We use corrugated QWIPs with different corrugation periods to extract α and g for different values of Vb. We find α≈0.1 μm−1 in the 6–12 μm range with small peaks at 8 and 9.8 μm for Vb>0 and 10 μm for Vb<0. g has a pronounced peak at 7.8 μm for both bias polarities and determines the line shape of the QWIP spectral responsivity. These results are attributed to insufficient electron transfer between the coupled QWs and to low tunneling probability of the longer wavelength photoelectrons. A modified QWIP structure has been proposed for complete switching of spectral responsivity peak when the bias voltage polarity is reversed.