Characterization and photocurrent spectroscopy of single quantum wells

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Abstract
GaAs/AlxGa1−xAs single quantum wells (SQWs) have been characterized by various spectroscopies and studied as electrodes in photoelectrochemical cells and in gold Schottky barrier structures. The techniques used were photoreflectance (PR), photoluminescence (PL), photocurrent (PC) spectroscopy, and impedance measurements. The energy level structure and well shape were best determined from PR data. The p doping of the buffer layer eliminated p–n junctions between the buffer layer and substrate and the inner AlxGa1−xAs barrier, thereby producing nearly ideal Mott–Schottky plots (no frequency dispersion or light dependence) so that the flatband potentials of these SQW electrodes could be well determined. Stark shifts in the PC spectra could also be seen if the buffer layer of the electrodes is doped p type. Very high quantum yields exhibited by SQW electrodes at room temperature with thick (270 Å) AlxGa1−xAs barriers are explained by thermionic emission. At low temperatures with Schottky barriers, other mechanisms, such as tunneling, dominate. Hot photoluminescence spectra were also obtained and the hot carrier behavior of SQWs is compared with multiple quantum wells.