Calculation of the densities of states of a-Si1-yCy(: H) alloys and comparison with measured X-ray spectra

A simplified model based on the Tight-Binding Coherent-Potential Approximat ion method that does not account for topological disorder, is employed to c alculate the s and p-symmetry densities of states of a-Si1 - yCy (:H) alloy s and crystalline SiC. Valence and conduction partial Si and C densities of states are obtained which allow us to observe that sp(3) hybridization is existing in these compounds. The calculations also show that in a-Si1 yCy a lloys, the total band gap increases by about 0.7 eV when going from y = 0.1 to y = 0.287 due to a progressive shift of both valence and conduction edg es below and above the top of the valence band, respectively. For crystalli ne SIG, the gap increases by about 1.5 eV with respect for example to a-Si0 .9C0.1. In hydrogenated alloys, the calculations display a steepening of th e valence and conduction band edges as compared to non-hydrogenated alloys confirming thus the 'healing' effect with H incorporation. The soft X-ray S i KB emission spectra are simulated by convolution of the occupied Si 3p di stribution with appropriate Lorentzian and Gaussian functions which account for the lifetime of the inner level involved in the Xray transition and th e instrumental function. respectively. The calculated spectra are in good a greement with experimental results on samples of similar nominal compositio n despite the fact that the theoretical model does not account for topologi cal disorder. (C) 2000 Published by Elsevier Science B.V. All rights reserv ed.