A microstructural model based on Si-centered tetrahedra is proposed for hydrogenated amorphous silicon nitride (a-${\mathrm{Si}}_{\mathit{x}}$${\mathrm{N}}_{\mathit{y}}$${\mathrm{H}}_{\mathit{z}}$) alloys. The dependence of the optical dielectric function ε=${\mathrm{\epsilon }}_1$+i${\mathrm{\epsilon }}_2$ of the a-${\mathrm{Si}}_{\mathit{x}}$${\mathrm{N}}_{\mathit{y}}$${\mathrm{H}}_{\mathit{z}}$ alloys on stoichiometry ([N]/[Si] ratio) and hydrogen content has been determined for (1) Si-rich a-${\mathrm{Si}}_{\mathit{x}}$${\mathrm{N}}_{1\mathrm{-}\mathit{x}}$ alloys (containing no hydrogen), using five tetrahedra, Si-${\mathrm{Si}}_{4\mathrm{-}\mathit{i}}$${\mathrm{N}}_{\mathit{i}}$ (i=0–4) and (2) N-rich a-${\mathrm{Si}}_{\mathit{x}}$${\mathrm{N}}_{\mathit{y}\mathrm{-}\mathit{z}}$(NH${)}_{\mathit{z}}$ alloys, again using five tetrahedra, Si-${\mathrm{N}}_{4\mathrm{-}\mathit{i}}$(NH${)}_{\mathit{i}}$ (i=0–4). Specific alloys of interest for which ε has been predicted using the Bruggemann effective-medium approximation include a-${\mathrm{Si}}_3$${\mathrm{N}}_4$ and a-Si(NH${)}_2$, amorphous silicon diimide. The predictions of the model for ε, the optical energy gap ${\mathit{E}}_{\mathrm{opt}}$, and the index of refraction n have been obtained considering both random bonding and phase separation in the alloys. These predictions are compared here with previous experimental results, while a more comprehensive comparison with experiment for some N-rich a-${\mathrm{Si}}_{\mathit{x}}$${\mathrm{N}}_{\mathit{y}}$${\mathrm{H}}_{\mathit{z}}$ films is presented in the following paper.

• Received 27 December 1989

DOI:https://doi.org/10.1103/PhysRevB.42.3658