Non-linear phenomena in semiconductor photoelectrocliemistry

The current response of semiconductor electrodes upon illumination has almost invariably been found to obey some simple rules. Anodic photoeffect is observed on n-type, cathodic photoeffect on p-type semiconductors and the photocurrent, measured under potentiostatic conditions, is proportional to light intensity. These observations have been understood in terms of some idealized models of charge formation and migration in the semiconductor and charge injection at the solid/liquid Interface. Now we report on a series of measurements, carried out on some lesser Known semiconductors, viz. HyWO₃ (hydrogen-tungsten bronze), HyNaxWO₃ (hydrogen-sodium-tungsten bronze) and B₆As where these simple rules do not hold. The non-linear dependence of photocurrent on light intensity seems to be the most general and at the same time the most striking observation. We rationalize our findings in terms of charge transport and injection kinetics.