SiOx nanowires with intrinsic nC-Si quantum dots: the enhancement of the optical absorption and photoluminescence

We report a very simple method for the fabrication of amorphous silicon rich oxide nanowires (a-SiOx NWs) with intrinsic nanocrystalline silicon quantum dots (nC-Si QDs) with a high density and controlled size, by thermally annealing thin films of nC-Si quantum dots embedded in the a-SiOx matrix, overcoated by an ultra-thin Au catalyst layer. The size and density of the Si-QDs in the basic matrix are controllable by changing the plasma parameters during the growth of the nC-Si/a-SiOx thin films. The diameter of the grown SiOx nanowires is controlled by merely varying the thickness of the Au-coating. The formation of the 1D NWs with rigid boundaries influences a shrinkage in the size of the intrinsic 0D QDs; the size-reduction of the QDs is more prominent in narrower NWs obtained from thinner catalyst layers. This unique quantum-dot/nanowire composite system demonstrates a significantly improved optical absorption and reduced reflection in the entire UV-visible range of the solar spectrum compared to its thin film structure, and those are again pronounced by reducing the dimension of the nanowires. The photoluminescence properties of this composite system demonstrate a strong room temperature emission band in the range of 400-600 nm with a peak at similar to 519 nm. The PL peak of the NW film undergoes a large blue shift by 150 nm from that of the annealed QD films which has been attributed to the reduction in the average size of the intrinsic nC-Si QDs during the growth of the a-SiOx NWs. These novel a-SiOx NWs with intrinsic nC-Si QDs, produced by a simple synthesis technique involving a solid-liquid-solid (SLS) growth process, deserve enough promise in the field of photovoltaics and light emitting devices.