Gallium phosphide/gallium arsenide phosphide strained-layer superlattice electrodes: effect of the terminating layer on photoelectrochemical properties

Pairs of strained-layer superlattices (SLS's) have been studied as photoanodes in photoelectrochemical cells (PEC's) employing aqueous ditelluride electrolyte. The SLS's are comprised of alternating layers of n-GaP and a n-GaAs/sub 1-x/P/sub x/ alloy (x approx. 0.6) with a total of 25 periods; the pairs are grown under matched conditions with one member terminating in the alloy composition and its counterpart in GaP. The pairs possess common bulk properties but different surfaces. While all samples examined gave good efficiencies for the conversion of 458- and 514-nm ultraband gap (E/sub g/ approx. 2.1 eV) monochromatic light to electricity (in some cases approx. 10%), the alloy-terminated samples gave consistently better efficiencies. Bulk and surface properties that may contribute to the superiority of the alloy-terminated samples are discussed. Photoaction spectra reveal the GaP-terminated samples to have an enhanced photoresponse near the band gap energy. Evidence that this feature is surface-localized is presented. Attempts to modulate the photoelectrochemical properties of a given SLS electrode by removing its original terminating layer are discussed.