Quantum-well infrared photodetector with voltage-switchable quadratic and linear response

We present a quantum-well infrared photodetector that allows us to switch between a quadratic and a linear detection mode. We employ an asymmetric detector design where intersubband transitions in a three-level system give rise to a quadratic power dependence down to very low excitation densities. Upon reversing the bias voltage, however, the intermediate subband acts as the ejection channel due to highly efficient tunneling, thus leading to a two-level system with linear photoresponse.