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Effects of magnetic field on the structural and optical properties of nanocrystalline silicon thin films deposited by helicon wave plasma chemical vapor deposition

Hydrogenated nanocrystalline silicon thin films have been deposited by helicon wave plasma chemical vapor deposition technique over the range of magnetic field strength (0-200Guass) using a mixture of silane and hydrogen gas. The effects of magnetic field on the structural and optical properties of the deposited films are characterized by Raman spectroscopy, x-ray diffraction and ultraviolet-visible transmittance spectroscopy. It has been found that the crystalline fraction and optical band gap Eg of the films change with magnetic field strength monotonically, while the deposition rate, the grain size and the B factor relating to the overall structural disorder reach a maximal value at 150 Guass. The variation of Raman scattering intensity ratio between silicon TA and TO mode indicates that the inner microstructure of the films becomes more orderly with increasing magnetic field strength until 150 Guass. The decrease trend of the optical band gap Eg and the changes of the B value with magnetic field strength from the ultraviolet-visible transmittance spectroscopy analysis are related to the increase of the grain size, the crystalline fraction and the hydrogen. The observed results have been discussed by the increase of hydrogen weak bond etching and dangling bond passivating effect with increasing magnetic field strength.