Amorphous SixC1-x:H single layers before and after thermal annealing: Correlating optical and structural properties

Amorphous SixC1-x:H single layers with varying stoichiometry were prepared using plasma enhanced chemical vapour deposition (PECVD). The as-deposited layers were annealed at different temperatures (T-a) from 500 to 1100 degrees C. The influence of annealing on layers with varying composition x was investigated by a variety of analytical techniques including photoluminescence (PL) spectroscopy, reflectance and transmittance measurements, grazing incidence X-ray diffraction (GIXRD) and Fourier transform infrared spectrometry (FTIR). Before annealing, PL measurements show a shift of the spectra to higher energies with increase in carbon content. Calculations of the optical bandgap by other groups confirm this trend. The FTIR investigations show in addition to the expected Si-C bonds also the formation of oxygen and hydrogen related bonds within the layers. After annealing, solely a broad PL signal appears at energies around 2.0 eV. This might be due to luminescence of defects, created by the incorporated amount of carbon and the evolution of crystalline phases in the layers. GIXRD measurements confirmed the formation of both Si NCs after 700 degrees C and SiC NCs after annealing at 1000 degrees C. The FTIR spectra exhibit a shift of the SiC absorption band and an increase in the Si-C bond density due to the crystallization of SiC. After annealing a hydrogen passivation was performed, which leads to a strong decrease in the PL intensity. However, annealed Si-rich films show a peak around 1.2 eV after H-passivation, which might originate from quantum confinement effects in Si NCs.