Effect of chlorine on the photoluminescence spectra of hydrogenated and chlorinated amorphous silicon prepared by glow discharge

Chlorinated and hydrogenated amorphous silicon films were prepared by glow discharge at various R.F. power. The photoluminescence spectra were measured as a function of temperature and plasma power. The temperature dependence of the integrated intensity of the luminescence band exhibits a feature in the 67–77°K temperature range. Using the luminescence, infrared, conductivity and compositional data we have ascribed this feature to a chlorine induced density of states in the band gap. Increasing the chlorine concentration in the sample results in a shift of the PL peak position (Ep) to higher energies and a broadening of the spectrum. Based on the band gap fluctuation model, and using the optical absorption data, we explained the Ep behaviour in terms of a redistribution of zero phonon transitions and a contribution, of compositional origin, from a change in the band gap energy.