Nonadiabatic transient behavior of quantum well photodetectors

Abstract

ABSTRACT In the presence of a time-dependent external source such as a bias electric field, an incident optical flux, or thetemperature, electrons in quantum well devices experience non-adiabatic transport through the barrier layer between twoadjacent quantum wells. This non-adiabatic transport process induces charge density fluctuations within each quantumwell, resulting in several seemingly unrelated transient phenomena. When a time-dependent electric field is applied tothe system, a dynamical breakdown ( i.e., the dark current is dominated by a dielectric displacement current) and a zero-bias residual dark current in the quantum-well photodetectors are predicted theoretically. If a chopped time-dependentoptical flux is incident on the system, a dynamical drop in the photo-responsivity with increasing chopping frequencyand an emission-current spike as the optical shutter is opened are predicted. Finally, as the device temperature is variedwith time, a counter-clockwise thermal hysteresis is found theoretically in the dark current curve as a function of thechanging temperature. Experimental confirmation of the above theoretical predictions is presented.Keywords: QWIP, quantum well detector, infrared detection, dark current, transient behavior