Quantization Effects in the Photocurrent Spectroscopy of Superlattice Electrodes

Strained-layer superlattices of [formual omitted], have been investigated as photoelectrodes in photoelectrochemical cells. Pronounced structure in the photocurrent spectra are observed that can be resolved into a series of Gaussian peaks that match the expected transitions between the theoretical energy levels of the GaAs quantum wells. The photocurrent spectra of various samples with the same quantum well width show marked variation in peak intensities, but with about the same peak positions. The sign of the photocurrent and the peak intensities depend upon photon energy, electrode potential, and electrolyte redox potential. The quantum yields were much higher for superlattices with 50-A barriers compared to 250-A barriers. A major conclusion is that electron injection into the electrolyte occurs from higher lying energy levels in the quantum wells, constituting a hot electron injection process. A qualitative model of the behavior of superlattice electrodes in photoelectrochemical cells is presented.