Nonlinear Photovoltaic Effect in Silver Bromide

The photovoltage of silver bromide single crystals has been measured at room temperature as a function of light intensity and wavelength. A two-part photoresponse was observed: a fast part with a risetime in the millisecond range, followed by a slower part with a response time of seconds. The fast response was nonlinear, the voltage varying approximately as the ⅔ power of the incident light intensity. A model based on a Dember-type effect was formulated to explain the results. Electrons are assumed to diffuse from the surface into the bulk, owing to their own concentration gradient, while holes are trapped near the surface to form interstitial silver ions which then move under the influence of the field of the electrons. The resulting differential equation was then solved with the aid of a computer. The slow response was ascribed to the effect of photodecomposition products on the initial photovoltage.