Charge transport in ultrathin silicon rich oxide/SiO2 multilayers under solar light illumination and in dark conditions

An extensive study on the electrical properties of Si nanocrystals under dark and solar light exposure in AM1.5G conditions is presented. The nanostructures have been obtained through chemical vapor deposition of multilayers of ultrathin silicon rich oxide/SiO2 films and subsequent thermal annealing. The electrical data demonstrate that the current transport in such systems is mediated by tunnel effect, and the lowest effective energy barrier limiting the carrier transport has been found to be 1.7 eV, well below the value's of 3.1 eV and 4.7 eV of free electrons and holes, respectively, at the standard Si/silicon dioxide interface. Under AM1.5G solar light illumination the contribution of the photocarriers increases with the voltage and above 60 V shows a trend toward saturation. A quantitative explanation of this saturation is discussed. Moreover, the photocarrier generation rate in the nanocrystals averaged over the solar spectrum region is evaluated.