This article presents a theory of the transient photoresponse of quantum well infrared photodetectors ͑QWIPs͒. As has been shown recently ͓M. Ershov, Appl. Phys. Lett. 69, 3480 ͑1996͔͒, the photocurrent in a QWIP in response to a step-like infrared illumination is composed of fast and slow transients. Analytical models for both fast and slow transients in the linear regime are proposed. The amplitudes and time constants of the transients are expressed in terms of the basic QWIP characteristics -capture time to the QWs, photocurrent gain, and differential conductivity of the emitter contact. Closed-form analytical expressions for the transient photocurrent in the time and frequency domains are obtained. The validity of the proposed analytical model is confirmed by comparison with numerical simulations.

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