Transient photocurrent overshoot in quantum-well infrared photodetectors

We report a strongly nonexponential behavior of the transient photocurrent in quantum-well infrared photodetectors (QWIPs) in response to a step-like infrared illumination. The transient photocurrent displays an overshoot on the time scale 0.1-1 ms at low temperatures (T < 70 K), exceeding the stead y-state photocurrent by as much as approximate to 50%. The overshoot behavi or is attributed to a nonlinearity of responsivity caused by the modulation of the electric field in QWIP under relatively high illumination power, wh en the photocurrent exceeds the dark current. This explanation is confirmed by the experimental data and numerical simulation. These effects can play an important role when QWIPs operate in nonlinear regimes, such as in a het erodyne mode or in low-temperature and low-background applications. (C) 200 1 American Institute of Physics.