Optical properties measurements of nanocrystalline silicon thin films

Abstract

Nanocrystalline silicon (nc-Si) thin films on 7059 corning glass substrate were prepared using Very High Frequency Plasma-Enhanced Chemical Vapour Deposition (VHF-PECVD) at different deposition temperatures. The nc-Si properties film were analyzed using spectroscopic ellipsometer, ultra violet (UV-VIS) spectrophotometer and luminescence spectrometer (PL). The thickness and optical constants of the films were investigated as a function of deposition temperature (Td) as Td increased the thickness and refractive index increased whereas the extinction coefficient decreased. Based on the transmission spectra, the nc-Si films found to have transmission percentage above 40% for the red visible spectrum wavelength. The photoluminiscence spectra of nc-Si films excited at 498 nm showed a single peak in the range of 1.84-1.95 eV (636-675 nm) and excited at 388 nm also showed a single peak in the range of 2.15-2.30 eV (539-579 nm). Both of these peaks were at energy higher than the band gap energy (Eband) obtained by using Tauc plot method which was around 1.7-1.8 eV. The peak energy was found to be shifted as Td changes. It was found that the decrease in Td acts to increase the values of Eband and the PL peaks showed red shift.