Electron transfer based voltage tunable two-color quantum-well infrared photodetectors

We present a detailed investigation of the temperature T dependence of photoresponse of voltage tunable two-color quantum-well infrared photodetectors (QWIPs) that are based on the transfer of electrons between coupled QWs under an applied bias V-b. For T less than or equal to 40 K, the peak detection wavelength switches from 7.2 mum under positive bias to 8.6 mum under large negative bias as electrons are transferred from the right QW (RQW) to the left QW (LQW). For T greater than or equal to 50 K, the short wavelength peak is not only present for both bias polarities but also increases rapidly with T while the long wavelength peak decreases rapidly with T. We investigate this temperature dependence by extracting absorption coefficient a and photoconductive gain g using corrugated QWIPs with different corrugation periods. The deduced absorption spectra indicate that the LQW population first increases and then decreases with increasing negative bias for T greater than or equal to 50 K. The deduced gain spectra show that short and long wavelength gain under negative bias exhibit a strong enhancement and reduction, respectively, with T above 50 K. We show that both these temperature dependences are caused by large thermal currents from the LQWs, which are designed for long wavelength detection and, therefore, have a significantly lower activation energy than the RQWs. (C) 2003 Elsevier B.V. All rights reserved.