We have performed an extensive series of measurements on symmetrical barrierbound‐to‐continuumand asymmetrical barrierbound‐to‐boundquantum well infrared photodetectors consisting of only asinglewell. We find that the behavior of the optical (e.g., responsivity) and transport properties (e.g., gain) as a function of bias is strikingly different from that of the usualmulti‐quantum well detectors. The simplicity of the structure has allowed an accurate theoretical calculation of the potential drops across each barrier, the photoinduced carrier depletion in the quantum well and therefore a detailed understanding of the device physics.