Peculiarities of optical absorption originating from boundaries of quasi-crystalline Si–C–O–N films deposited on a SiO 2 amorphous-like substrate

Abstract

The ultraviolet (UV)-absorption spectra, originating from boundaries formed by partially crystallised Si–C–O–N film deposited on a SiO 2 substrate, were simulated using a semi-empirical quantum-chemical parametrisation method (PM3). Several Si–C–O–N modelled structural clusters, covered with different types of atoms, namely: carbon, silicon, oxygen and hydrogen, were considered. The initial geometry of the investigated clusters was built following extended X-ray absorption fine structure experimental data. Each of the considered clusters was geometrically optimised by total energy minimisation to simulate the influence of the interface, formed between the films and substrate, on the electronic parameters of the investigated structure. Correlation was found between the total energy of a particular cluster, the values of the HOMO-LUMO energy gap splitting and the spectral features of the electronic density of states (DOS). A substantial influence of external sheets on spectral positions in the DOS was found. For the UV-absorption spectra, additional spectral maxima did appear upon changing of the Si–C–O–N covering sheet. The present work is devoted to a study of the influence of the cluster's boundary conditions (surrounding chosen cluster shell) on electronic properties and optical absorption of the corresponding Si–C–O–N clusters.