Structural and electrical properties of polycrystalline silicon films deposited by hot-wire CVD

Abstract

The polycrystalline silicon (poly-Si) films are deposited on low-temperature glass substrate by hot-wire CVD. The SiH 4 gas flow rate {F(SiH 4 )} is a critical parameter both for deposition rate and for crystalline properties. The poly-Si films deposited at low F(SiH 4 ) with moderate deposition rate (about 3 μm/h) have superior crystalline properties and crystalline volume fraction that exceeds 90%. The films also have natural texture structure on the surface that is strongly recommended in thin-film solar cells in order to obtain high current density by increasing incident light trapping. By increasing F(SiH 4 ) to 10 sccm, the high deposition rate (20 μm/h) is obtained, but crystalline properties deteriorated in these samples. However, these films have high potentials for thick (20-30 μm) solar cell applications due to the high deposition rate and enhanced grain growth; average grain sizes are larger than that of low-F(SiH 4 ) samples although small nano-sized grains still exist, by which crystalline volume fraction was <70%. The secondary ion mass spectroscopy and Fourier transform infrared spectroscopy analysis showed that the films have considerable amount of O and C within the films and this is originated from impurity penetration during storing the samples in atmosphere.