Negative photoconductivity in SiO2 films containing Si nanocrystals

Negative photoconductivity is reported in metal-insulator-semiconductor str uctures containing Si nanocrystals produced by ion implantation and anneali ng. Under forward bias, the current is reduced when the sample is illuminat ed with ultraviolet light whilst under reverse bias it is increased. No suc h change is observed in structures that have not been ion implanted. This e ffect is explained by charging of nanocrystals in the oxide layer by photoi onization of electrons. The positively charged nanocrystals screen the appl ied bias voltage leading to a reduction in current at a given voltage. This effect, if larger than the current increase caused by the photoexcitation of carriers in the accumulation layer, gives rise to the observed negative photoconductivity. (C) 1999 American Institute of Physics. [S0003-6951(99)0 1526-0].