Optical properties of Se or S-doped hydrogenated amorphous silicon thin films with annealing temperature and dopant concentration

We report the effects of the thermal annealing and dopant concentration on the optical properties of Se or S-doped hydrogenated amorphous silicon thin films. The Se and S-doped a-Si:H (a-Si,Se:H and a-Si,S:H) thin films were prepared by glow discharge plasma enhanced chemical vapor deposition (GD-PECVD) on 7059 corning glass. The films were subsequently annealed in vacuum in the temperature range from 100 to 500 °C. Influence of doping and annealing was examined by means of optical transmission spectroscopy of the films in the wavelength range of 300–1100 nm taken at room temperature. The absorption coefficients and refractive indices decreased as the annealing temperature increased from 100 to 300 °C and then increased again as the annealing temperature further increased to 500 °C, while the highest bandgap was observed at 300 °C for all of the samples. For a given dopant concentration bandgap was observed to be higher in a-Si,S:H than a-Si,Se:H thin films.

Research highlights▶ The optical constants of Se and S-doped a-Si:H thin films were calculated from transmission spectra with respect to annealing temperature and dopant concentration. ▶ The annealing temperature at which the best optical constants were obtained for the Se and S-doped a-Si:H thin films was experimentally observed to be 300 °C. ▶ The values of the absorption coefficients were observed approximately 1 order of magnitude higher in the Se-doped a-Si:H thin films than in the S-doped a-Si:H thin films. ▶ The value of the bandgap was observed to be smaller in the a-Si,Se:H films than in the a-Si,S:H thin films.