Electronic structure of carbon-rich a-Si1-xCxHy alloys: The role of hydrogen and graphitic carbon
(EN)
Katsoulakos, P
(EN)
Xanthakis, JP
(EN)
Orphanides, P
(EN)
We calculated the electronic structure of carbon-rich a-Si1-xCxHy, an alloy for which there is conflicting experimental evidence for the degree of disorder and the fraction of graphitic carbon atoms present. Our calculation takes into account valence disorder due to carbon and hydrogen as well as short-range order effects. We deduce that, if the alloy is heavily hydrogenated, then Si-Si bonds exist in considerable amount up to x = 0.75 at least. Furthermore the fraction of graphitic carbon atoms increases slowly up to the value of x at which a maximum in the band gap occurs and then it increases rapidly as some experiments seem to confirm. Our calculated band gap as a function of x is in reasonable agreement with experiment and our peaks in the density of states (DOS) correlate well with the peaks of the photoemission spectra whose orbital character we can deduce. We note that our conclusion on the presence of Si-Si bonds is independent of our method of calculating the DOS and derives from our matching of atoms to the corresponding bonds. Finally estimates of the fracton of graphitic atoms at each x are made.
(EN)
