The relation between recombination at interface states and the anomalouslysmall exponent of the current-illuminance characteristic in microcrystalline silicon

The recombination of nonequilibrium charge carriers in p-Si doped lightly w ith boron was analyzed; the samples were obtained by high-frequency decompo sition of silane diluted heavily with hydrogen under conditions of a high h igh-frequency power. The columnar formations composed of microcrystallites are typical of the structure of such a material. It was established that, i n a limited temperature range, the dominant recombination mechanism may be related to recombination at intercolumnar boundaries in combination with tu nneling and partial thermal activation. Such recombination leads to an anom alously small exponent in the current-illuminance characteristic gamma 0.3. The suggested model makes it possible to calculate the temperature depende nces of gamma for various levels of doping of the material acid predicts a decrease in the efficiency of doping and an increase in the defect concentr ation in the material with an increasing concentration of introduced boron. The recombination mechanism changes at elevated temperatures; as a result, the recombination at the boundaries governed by the Shockley-Read statisti cs becomes prevalent. Tunneling-related recombination within the columns is dominant at low temperatures. Both mechanisms lead to an increase in gamma to conventional values (Y approximate to 0.7). (C) 2001 MAIK "Nauka/Interp eriodica".