CAPTURE DYNAMICS AND FAR-INFRARED RESPONSE IN PHOTOVOLTAIC QUANTUM-WELL INTERSUBBAND PHOTODETECTORS

Recent progress in photovoltaic quantum well intersubband photodetecto rs (QWIP) makes these devices suitable for high-performance imaging an d heterodyne detection. We report on investigations concerning the bas ic physics of the transport mechanism, the dynamical behavior, and the further optimization of these structures. GaAs/AlAs/AlGaAs double-bar rier QWIPS designed for 3-5 mu m wavelength operation provide an inter esting model system to study the dynamical aspects of the photovoltaic response. We find strong evidence that carrier transfer across the Al As barriers mainly occurs due to Gamma-X intervalley scattering, even for AlAs layer thicknesses of 1-2 nm. We also discuss experimental res ults on photovoltaic QWIPs operating in the 8-12 mu m regime. In these structures, photovoltaic operation is achieved using a combination of single-barrier quantum wells with built-in space-charge fields. We re port on a photovoltaic QWIP with a cutoff energy of 118 meV and a zero -bias detectivity of 2.5 x 10(9) cm root Hz/W, which is only three tim es less than the detectivity of a photoconductive QWIP with the same c utoff energy. (C) 1996 Academic Press Limited