Determination of the electron capture time in quantum-well infrared photodetectors using time-resolved photocurrent measurements

We have investigated the transport properties of optically excited electrons in a 100 period InGaAs/GaAs-quantum well infrared photodetector. The electrons were excited by femtosecond-infrared laser pulses and the transient photocurrent was recorded in the picosecond regime. We have carefully analyzed the measured photocurrent transients taking into account both the capture time τc and the transit time τtrans. Our experimental results allow us to determine τc, which increases from 10 ps at 5 kV/cm to about 20 ps at 20 kV/cm. We have also measured the noise gain in order to determine the transit time and the drift velocity. The dynamic parameters extracted from our measurements are consistent with values from the literature.