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The optical constants (n =n +ik, el -nk, e2 --2nk) of a series of amorphous hydrogenated silicon-carbon alloy films (a-Sil C:H) have been determined for photon energies between 1.5 and 4.75 eV. These films have been prepared via the rf glow-discharge decomposition of SiH4 and CqH2.The index of refraction n at 1.5 eV increases smoothly from n =1.67 for a-C:H (~=1) to n =3.18 for a-Si:H (x =0), while the optical energy gap Eopt reaches a maximum value of 2.68 eV for a carbon fraction of x =0.68. The films in this alloy series are proposed to be macroscopically homogeneous, while having a heterogeneous microstructure. Their optical response has been modeled, via the Bruggemann effective-medium approximation (EMA), as arising from three amorphous components: polymeric (a-CH, m -2), graphitic (a-C), and tetrahedral (a-Si:C:H), and a void component. A Siand C-centered tetrahedron model developed in the preceding paper has been used to predict the optical response of the amorphous tetrahedral component as a function of its composition. This EMA approach based on four components in the films gives a good description of the observed dependences of el and e2 on composition and provides a convincing demonstration that the appearance of the amorphous graphitic component in the films limits the attainable value of E"p, in this alloy series as the carbon content increases. In addition, the model provides strong evidence that complete chemical ordering with homogeneous dispersion exists within the amorphous tetrahedral (a-Si:C:H) component across the entire alloy series.

Silicon nitride films of varying composition have been deposited with nitrogen dilution onto p-type silicon substrates at 250 °C by plasma enhanced chemical vapor deposition technique. Careful and detailed capacitance–voltage (C–V) measurements have been undertaken in the metal-insulator-semiconductor configuration. Silicon-rich films are found to exhibit large symmetric hysteresis loops in the C–V curve while the nitrogen-rich films display much smaller asymmetric hysteresis loops. Furthermore, the minimum interface state density is observed to decrease with the increase in nitrogen to silicon ratio. In this study we have observed that the concentration of both electron as well as hole traps are much lower for the nitrogen-rich films.

The nanocrystalline silicon embedded in amorphous silicon carbide matrix was prepared by varying rf power in high vacuum plasma enhanced chemical vapor deposition system using silane methane gas mixture highly diluted in hydrogen. In this paper, we have studied the evolution of the structural, optical, and electrical properties of this material as a function of rf power. We have observed visible photoluminescence at room temperature and also have discussed the role played by the Si nanocrystallites and the amorphous silicon carbide matrix. The decrease of the nanocrystalline size, responsible for quantum confinement effect, facilitated by the amorphous silicon carbide matrix, is shown to be the primary cause for the increase in the PL intensity, blueshift of the PL peak position, decrease of the PL width (full width at half maximum) as well as the increase of the optical band gap and the decrease of the dark conductivity.

The optical properties of the hydrogenated amorphous silicon carbon alloy films, prepared by plasma enhanced chemical vapor deposition technique from silane and methane gas mixture diluted in helium, have been investigated using variable angle spectroscopic ellipsometry in the photon energy range from 0.73 to 4.59 eV. Tauc–Lorentz model has been employed for the analysis of the optical spectra and it has been demonstrated that the model parameters are correlated with the carbon content as well as to the structural properties of the studied films.