Configurational statistics in a-${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{N}}_{\mathrm{y}}$${\mathrm{H}}_{\mathrm{z}}$ alloys: A quantitative bonding analysis

The composition of hydrogenated silicon nitride films produced either by plasma-enhanced chemical-vapor deposition (PECVD) with 0.01≤[${\mathrm{NH}}_3$]/[${\mathrm{SiH}}_4$]≤20 in the 220–320-°C temperature range or by low-pressure chemical-vapor deposition at 800 °C was determined by elastic-recoil-detection techniques and compared with the relative and absolute atomic densities deduced from x-ray photoelectron spectroscopy and optical measurements in the infrared (ir) range. The [N]/[Si] ratio of PECVD samples followed a square-root dependence on [${\mathrm{NH}}_3$]/[${\mathrm{SiH}}_4$] over most of the gas-ratio range. We propose original calibrations of most of the ir-absorption bands observed in these samples over the 600–3600-${\mathrm{cm}}^{\mathrm{-}1}$ range, and we derived the experimental bond statistics by assuming complete valence satisfaction. In particular, the oscillator-strength factor of each of the six components of the SiH stretching peak was determined. The detailed statistics of all the hydrogenated configurations established for the first time in such a silicon-based ternary alloy are then compared to those expected to those expected for a random-bonded network. The most striking deviations from configurational randomness were observed at low nitrogen contents where more than two out of three silicon neighbors of a given nitrogen atom are monohydrogenated. Nitrogen atoms are found to have at least one monohydrogenated silicon nearest neighbor in all samples up to [N]/[Si]=1.1. The generality of such a second-neighbor correlation in hydrogenated III-IV amorphous alloys is also discussed.