Long-wavelength infrared absorption and photoconductivity in gallium antimonide-aluminum antimonide superlattices

Bandgap-engineered III-V semiconductors form an active research area in the field of long-wavelength infrared detectors, due to their potential for revolutionizing the infrared imaging technology in the mid-to-far-infrared region of the spectrum. Infrared detectors based on intersubband transitions in quantum wells have proven especially important in this fast-growing field. In particular, quantum well detectors that operate under normal incidence are becoming increasingly popular due to their potential for improved quantum efficiency. The GaSb-AlSb quantum well system offers the possibility for normal-incidence long-wavelength detection, due to peculiarities in the band structure of GaSb quantum wells. The work described in this dissertation presents a detailed study of infrared absorption and photoconductivity in n-type GaSb quantum wells with AlSb barriers grown by molecular beam epitaxy (MBE).; Using Fourier transform infrared (FTIR) spectroscopy, intersubband absorption under normal-incidence radiation has been demonstrated in the superlattices over a range of wavelengths from 4-17 {dollar}mu{dollar}n. Very strong absorption coefficients were observed, in excess of 8000 cm{dollar}sp{lcub}-1{rcub}{dollar}. The model for the intersubband transition energies as a function of quantum well parameters is compared with experimental data.; Absorption is only part of the story when trying to make an infrared detector. The photo-excited electrons must somehow be collected in the form of current. Issues important in the collection of photo-excited electrons will be discussed, and a method with the potential for improving collection by tailoring the intersubband energies will be introduced. Infrared photoresponse measurements as a function of photon energy have been performed. Normal-incidence infrared photoresponse due to intersubband transitions in GaSb quantum wells was observed.; In addition to the photoresponse from intersubband absorption, an unusual photovoltaic effect was observed in the quantum well samples, giving rise to a photocurrent at zero voltage. During the course of this study, it was found that the photovoltaic property appears independent of the quantum well parameters, but depends on doping and barrier composition, and is likely associated with traps in the barriers.