ON THE INCREASE OF THE PHOTOCURRENT QUANTUM EFFICIENCY OF GAP PHOTOANODES DUE TO (PHOTO)ANODIC PRETREATMENTS

It has been found that the photocurrent quantum efficiency of n-type GaP single crystal electrodes illuminated with visible light (green-blue) increases markedly as a consequence of photoanodic etching or polarization at very positive potentials. The origins of this increase have been systematically investigated. Two effects are of importance. Photoanodic etching leads to a roughening of the surface; as a consequence the incident light is scattered and absorbed more effectively in the region of the solid in which electron-hole pairs are separated by diffusion or migration. In addition, photoanodic current flow or severe positive polarization lead to a considerable increase of the diffusion length of the photogenerated holes. This effect is attributed to passivation of hydrogen-related recombination centers by hole capture and subsequent release of hydrogen.