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

The recombination of nonequilibrium charge carriers in p-Si doped lightly with boron was analyzed; the samples were obtained by high-frequency decomposition of silane diluted heavily with hydrogen under conditions of a high high-frequency power. The columnar formations composed of microcrystallites are typical of the structure of such a material. It was established that, in a limited temperature range, the dominant recombination mechanism may be related to recombination at intercolumnar boundaries in combination with tunneling and partial thermal activation. Such recombination leads to an anomalously small exponent in the current-illuminance characteristic gamma 0.3. The suggested model makes it possible to calculate the temperature dependences 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 concentration 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 statistics 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/Interperiodica".