New quantum well long-wavelength (λ=10 μm) detectors and novel superlattice transport physics

The authors have demonstrated the first 10 μm detector based on bound-to-continuum absorption in doped GaAs/AlGaAs quantum wells which have been designed to contain only one bound state. The linear voltage dependence of the responsivity is strikingly different from these previous intersubband tunneling detectors, containing two bound states in the quantum well, which show an exponential tunneling voltage dependence. The hot electron mean free path (1700 Å) for transport above the superlattice as well as the mobility and carrier lifetime (2 ps) have been determined. The authors have measured the continuum infrared (λ ~10 μm) photoconductivity spectrum for a dual-bound-state intersubband absorption photoexcited tunneling quantum-well detector. The line shape is broadened and asymmetrical with respect to the zero-bias Lorentzian absorption spectrum. They report intersubband absorption experiments in doped InGaAs/InAlAs multiquantum well superlattices and observe a resonance peak at a wavelength of λ=4.4 μm, which is in good agreement with theory. The authors have measured a novel negative differential photoconductance (at 10 μm) in an alternately doped multi-quantum-well structure. From this measurement, the density of the electrons dynamically stored in the undoped wells can be deduced at different external biases