Impact of transit-time and capture effects on high-frequency performance of multiple quantum-well infrared photodetectors

An analytical model of multiple quantum-well photodetectors (QWIP's) is proposed and used to evaluate their high-frequency performance. The model accounts for the electron photoexcitation from the QW's, capture into them and drift of the photoexcited electrons across the barriers. The frequency-dependent responsivity and the gain-bandwidth efficiency are derived as functions of the QWIP parameters. It is shown that the responsivity roll-off and 3 dB bandwidth are determined by the electron transit-time and capture effects, so that the main factors limiting the QWIP high-frequency performance are the number of the QW's and the rate of the electron capture into them. It is predicted that the gain-bandwidth efficiency weakly depends on the number of the QW's and capture parameter.