STRUCTURAL, COMPOSITIONAL AND OPTICAL-PROPERTIES OF HYDROGENATED AMORPHOUS-SILICON CARBON ALLOYS

Steady-state optical modulation spectroscopy (OMS) measurements have been carried out on well characterized hydrogenated amorphous silicon carbon alloy layers. A series of samples with methane-to-silane gas flow ratios varying from 0.1 to 0.7 was deposited at 250-degrees-C using the conventional r.f glow-discharge deposition method. In order to characterize the material, we investigated the structural, compositional and optical properties of these alloys by means of Fourier-transform infrared spectroscopy, Raman spectroscopy, elastic recoil detection, Rutherford back-scattering spectrometry and optical transmission and reflection spectroscopy. OMS measurements were performed at room temperature and at T almost-equal-to 50 K. From room-temperature data the energy positions of the dangling-bond states were deduced. Transition energies involving D0 states are found to shift to higher values with increasing carbon content, while transition energies involving D- states remain almost constant. At lower temperatures, band-tail contributions become dominant in the OMS spectrum. From the photoinduced absorption part of these low-temperature OMS data the exponential band-tail parameter E0 has been determined. We observed an increase in E0 with increasing carbon content.