Negative photoconductivity in SiO₂ films containing Si nanocrystals

Metal-insulator-semiconductor structures containing Si nanocrystals were fabricated by evaporating a Au layer onto the surface of ion implanted SiO₂ films and applying an In-Ga eutectic to the sample after oxide layer removal to form a rear side contact. As evidenced from measured current-voltage characteristics, the structures exhibit negative photoconductivity. UV illumination reduces the current under forward bias, whilst increases it under reverse bias. The reduced current is attributed to electron photoionization which charges the nanocrystals positively leading to screening of the applied bias voltage.