Tailoring mid- and long-wavelength dual response of InAs quantum-dot infrared photodetectors using InxGa1−xAs capping layers

We report on the tailoring of detection bands of InAs quantum-dot infrared photodetectors (QDIPs) using InxGa1−xAs capping layers and on the realization of voltage-tunable two-color QDIPs for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) detection. QDIPs having 2.0 ML InAs QDs capped by 20 ML In0.15Ga0.85As layer show bias-dependent photocurrent peak positions in the LWIR regime (∼8–9 μm) which are redshifted with respect to those (∼5–7 μm) in the counterpart QDIPs without InxGa1−xAs capping layers. QDIPs having 2.5 ML InAs QDs capped by a 30 ML In0.15Ga0.85As layer have a bimodal QD size distribution and show voltage-tunable MWIR (∼5.5–6 μm) and LWIR (∼9–11 μm) photoresponse. At low bias, MWIR photoresponse is dominant whereas with increasing bias, the LWIR photoresponse becomes dominant.