Short-wavelength spectral response properties of semiconductor/liquid junctions

We report the first measurements of photocurrent quantum yields for semiconductor/liquid junctions in the short-wavelength region of the spectrum (200-600 nm). The key feature of this wavelength region is the short penetration depth for the absorbed photon (less than 100 Å), which allows measurement of the majority carrier collection velocity. Spectra have been obtained for semiconductor/liquid, semiconductor/metal, and semiconductor/insulator/metal junctions. For all semiconductors studied (n-Si, p-Si, n-GaAs, n-InP, a-Si:H), the spectral responses of the liquid junctions showed higher quantum yields than the metal junctions, indicating greater majority carrier losses at the metal junctions. This general trend was independent of redox species, solvent, supporting electrolyte, and metal overlayer. The spectral response data can also be used to distinguish Schottky barrier behavior from electrocatalytic behavior of metal overlayers, and this approach has been used to study several semiconductor/metal film junctions in contact with electrolytes.