Interband and intersubband transitions in indium arsenide doping superlattices studied by absorption, nonlinear absorption and photoconductivity spectroscopies

Doping superlattices ('nipi' crystals) have been grown (by MBE on GaAs) and characterized in narrow-gap binary InAs for the first time. Low-temperature absorption measurements demonstrate effective optical bandgap lowering by >25%, giving long-wavelength thresholds of approximately=4.2 mu m in cooled trial photoconductive detectors. Long minority carrier lifetimes (100-400 mu s) and low power nonlinear optical saturation results confirm the character of the nipi potential and measured data agree well with an envelope-function calculation of the electronic subband structure. Intersubband transitions are detected and modelled in asymmetric InAs nipi samples and indicate the possibility of improved 10 mu m detectors in this material.