ELECTRONIC-STRUCTURE OF SI-RICH ASI1-XCXHY ALLOYS

We have calculated the electronic structure of amorphous hydrogenated Si-rich Si1-xC(x)H(y) alloys paying particular attention to methylated Si, i.e. alloys produced at low deposition power with CH3 configurati ons only and no C-C bonds. The configurational averaging method we use produces densities of states (DOS) which are not only a function of t he compositional indices but also of the short-range order (SRO) param eters. By varying the DOS with respect to these parameters we are led to deduce the origin of all the experimental XPS peaks including the o ne at - 14 eV which is assigned to Si(s) and C(s) orbitals in Si-C bon ds. The calculated band gaps of the alloys produced at high deposition power are in good agreement with experiment and tentatively point to a small to medium degree of disorder. On the other hand the calculated band gaps of methylated Si is in remarkable agreement of x < 0.25 whe n the CH3 configuration is known to prevail but deviates considerably from the very high recently published experimental band gaps near x ap proximately 0.4 suggesting that the model of methylated Si may require modification for these values of x.