TETRAHEDRON MODEL FOR THE OPTICAL DIELECTRIC FUNCTION OF HYDROGENATED AMORPHOUS-SILICON NITRIDE ALLOYS

A microstructural model based on Si-centered tetrahedra is proposed for hydrogenated amorphous silicon nitride (a-SixNyHz) alloys. The dependence of the optical dielectric function =1+i2 of the a-SixNyHz alloys on stoichiometry ([N]/[Si] ratio) and hydrogen content has been determined for (1) Si-rich a-SixN1-x alloys (containing no hydrogen), using five tetrahedra, Si-Si4-iNi (i=04) and (2) N-rich a-SixNy-z(NH)z alloys, again using five tetrahedra, Si-N4-i(NH)i (i=04). Specific alloys of interest for which has been predicted using the Bruggemann effective-medium approximation include a-Si3N4 and a-Si(NH)2, amorphous silicon diimide. The predictions of the model for , the optical energy gap Eopt, 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-SixNyHz films is presented in the following paper. © 1990 The American Physical Society.