Optical and Structural Properties of Ammonia-Free Amorphous Silicon Nitride Thin Films for Photovoltaic Applications

Hydrogenated amorphous silicon nitride (a-SiNx:H) thin films have been deposited through the green chemistry route using silane (SiH4) and nitrogen (N2) as process gases with SiH4 flow being variable and N2 flow being constant without the use of pollutant and corrosive ammonia (NH3) by the plasma-enhanced chemical vapor deposition technique at 13.56 MHz. Fourier transform infrared spectroscopy analysis shows various possible vibrational modes of Si-H, Si-N, and N-H bonds present in the film. Raman spectroscopy is performed on these samples to calculate volume fractions corresponding to amorphous phases present in the a-SiNx:H films. The refractive index (η) values are calculated using Swanepoel's method, which are in the range of 2.89 to 3.17. The thickness of the deposited films has been evaluated using transmission spectra. Absorption coefficient and band gap (E g) values are obtained from optical absorption studies. An increase in the E g and a decrease in the η value have been observed for the samples grown with decreasing SiH4 flow.