High Photovoltages in Silicon and Silicon Carbide Films and Their Origin from a Trap-Induced Space Charge

Publisher Website
Google Scholar
Abstract
Photovoltages were observed in thin films of silicon and silicon carbide which were not uniform in thickness. In some cases, the photovoltages exceeded the band gap. The photovoltages were retained by the film after removal of the light and decayed exponentially with time constants of the order of tens of seconds. The films were capable of acquiring persistent space charges upon application of an external voltage. The space charges decayed exponentially after removal of the applied voltage with time constants similar to that of the decay of the photovoltages. The photovoltages seemed related to the nonuniformity of the film, increasing with increasing nonuniformity. These results were interpreted to mean that the photovoltage is due to a space charge produced by a nonuniform distribution of trapped minority carriers, and a mathematical formulation was given to this concept. The temperature, light intensity, and carrier lifetime dependence of the photovoltage were in qualitative agreement with this concept. The temperature dependence of the decay constants of the photovoltage could also be interpreted satisfactorily in terms of this theory. A remarkable correlation between the photovoltage and the apparent resistance of the films was noted. It is suggested that the high photovoltages observed in films of other materials may have an origin similar to that discussed here.