Purely intrinsic poly-silicon films for n-i-p solar cells

Polycrystalline silicon films have been prepared by hot wire chemical vapor deposition (HWCVD) at a relatively low substrate temperature of 430° C at a high growth rate (>5 Å/s) by optimizing the hydrogen dilution of the silane feedstock gas, the gas pressure and the wire temperature. The optimized material has 95% crystalline volume fraction with complete coalescence of grains. The grains with an average size of 70 nm have a preferential orientation along the (220) direction. Large structures up to 0.5 µ m could be observed by atomic force microscopy (AFM). An activation energy of 0.54 eV for the electrical transport and a low carrier concentration (