Direct Current in Non-steady-state Photovoltaic Effect

A new non-steady-state photovoltaic effect in a uniform bipolar semiconductor doped with impurities changing their charge state under illumination is predicted. Direct electric current is shown to arise in the ring-shaped uniform bipolar semiconductor sample illuminated by a moving light pattern. The physical basis of the effect is the simultaneous change of the charge carriers density and mobility, as well as the difference in lifetimes of the ionized impurities, charge carriers and the light pattern traveling time along the semiconductor sample.

The expression for the short-circuit photocurrent in the semiconductor ring is obtained under the quasineutrality assumption, its dependence on the light pattern parameters, as well as on the semiconductor properties and on the sample size is analyzed. It is shown that there are the optimum light pattern velocity and the optimum semiconductor length providing the largest magnitude of the photovoltaic effect. It is found that the short circuit photocurrent is proportional to the squared amplitude of the light intensity modulation at its arbitrarily small value. The photocurrent is also sensitive to the mean intensity of light pattern and may change its sign with increasing the mean intensity of the incident light. Under a sufficiently strong illumination the photovoltaic effect vanishes.