Anomalous photovoltaic effect in nanocrystalline Si/SiO2 composites

We have observed an anomalous photovoltaic effect in films of Si nanocrystals embedded in SiO2. Using conductive-probe atomic force microscopy and global transport measurements, we found, close to the percolation threshold of the Si crystallite phase, a large photovoltaic effect of up to about 7 V. Following the dependence of this effect on the size of the Si nanocrystals and on the relative tip position with respect to the counterelectrode, we suggest a model based on charge separation of excited electron-hole pairs governed by the size-dependent quantum confinement and charging energies. (c) 2008 American Institute of Physics.