Decomposition of Silicon rich oxide films by Diode Laser processing to fabricate Sponge-like Si-SiO2 nanocomposites for photovoltaics

Absorber layers consisting of nanostructured Si are candidates for next generation thin film Si solar cells. For this aim, Si-SiO2 nanocomposites with crystalline sponge-like Si are promising materials since their band gap is increased by quantum confinement and since they provide electrical interconnectivity. Such nanosilicon has recently been fabricated by annealing of non-reactively sputter deposited SiOx films (x< 1). It is formed by solid state phase separation into a percolated network of Si nanowires. The phase separation is usually accompanied by crystallization of Si. Here, SiOx layers have been grown by ion beam sputter (IBS) as well as by reactive magnetron sputter (RMS) deposition. Phase separation into Si-SiO2 nanocomposites has been achieved by scanning a diode laser line source with dwell times in the ms range and compared to a furnace treatment lasting ~106 times longer. Furnace annealing of IBS and RMS deposited layers result in sponge-like and filament-like silicon nanostructures, respectively. Laser processing of IBS layers leads to morphologies self-similar to furnace annealed samples, but scaled up by a factor of ~10. This indicates that the faster phase separation mechanism occurs in the liquid state. It is expected that laser processing of RMS layers will result in sponge-like morphologies too, and not filament like ones due to the liquid state phase separation.