Effects of high hydrogen dilution ratio on optical properties of hydrogenated nanocrystalline silicon thin films

Hydrogenated nanocrystalline silicon thin films were prepared by plasma enhanced vapor deposition technique. In our experiment, hydrogen dilution ratio R_H was changed mainly, while the other parameters, such as the radio frequency power, the direct current bias value, the chamber pressure, the total gas flow and the substrate temperature were kept constant. The film's surface topography was gained by AFM. The chemical bond was confirmed by Fourier transform infrared spectra. The optical properties were characterized by transmission spectra. To consider absorption peak of stretching vibration mode of SiH₃ at 2140 cm⁻¹ and to reduce the calculation error, a hydrogen content calculation method was proposed. Effects of hydrogen dilution ratio on the deposition rate v and hydrogen content C_H were investigated. The bonding mode and the force constants k of chemical bond, the structural factor f in films were changed by high hydrogen dilution ratio, which gave rise to the shift of absorption peak of infrared stretching mode and the decrease of optical band gap E_g.