Terahertz operation of quantum-well intersubband hot-electron phototransistors

A novel infrared photodetector utilizing intersubband electron transitions and plasma wave excitation in a quantum well (QW)-the QW intersubband hot-electron phototransistor (MEPT)-is proposed and evaluated. It is shown that the excitation of standing plasma waves in the QW base by incident modulated infrared radiation can result in resonant response of IHEPT's. The plasma resonance peaks of the linear responsivity of IHEPT's with a base contact spacing of about 1 mu m correspond to the terahertz range of modulation (signal) frequencies. The resonant peaks of the responsivity can be tuned by the biasing voltage. The peak value of the IHEPT resonant responsivity can be of the order of the steady-state responsivity of standard QW intersubband infrared photodetectors, significantly exceeding the high-frequency performance of the latter. Relatively large values of the IHEPT resonant responsivity are associated with strong injected current stimulated by the plasma waves in the QW-base. Finally, it is shown that the nonlinear dependence of the injected current on the potential of the QW base results in the variation of the de current with changing signal amplitude. The nonlinear response current as a function of the modulation frequency also exhibits resonant behavior with the peaks at the plasma resonance frequencies and can be used for the detection of the signal component envelope.