Fabrication of site specific amorphous/nanocrystalline silicon composite thin film for solar cells

The absorption properties of amorphous silicon (α-Si) and the electron transport properties of nanocrystalline silicon are combined in a novel composite material for thin film silicon solar cells. In this work a composite film composed of α-Si with site specific areas of nanocrystalline material was created. Al was deposited through a SiO2 template containing nanometer sized apertures with an approximate diameter of 250 nm onto an α-Si film supported by a <;100>; crystalline silicon substrate. It was then annealed at 350°C. The annealing caused crystallization only at sites where the Al was in contact with the α-Si surface. The AIC created site specific three dimensional nanocrystalline structures embedded in a thin film of α-Si. After grain boundary passivation these nanocrystalline sites will provide pathways for charge carriers that are less defect dense than the α-Si film. TEM samples were fabricated from the composite film utilizing the focus ion beam. The growth characteristics of these 3D nanostructures and the α-Si thin film were characterized utilizing ESEM and the TEM.