OXYGEN EFFECT ON OPTICAL-PROPERTIES OF NANOSIZE SILICON CLUSTERS

Optical absorption and light emission of oxygen-incorporated small sil icon (Si14H24) clusters as a function of oxygen content were theoretic ally studied using a self-consistent semiempirical molecular orbital m ethod (modified neglect of diatomic overlap-parametric method 3). Two different models of oxygen incorporation were considered. Changes in t he appropriate energies were traced when oxygen atoms were introduced either to the cluster surface (OH-group passivation) or inside the clu ster. An increase of the number of oxygen atoms both at the surface an d inside the cluster results in the decrease of the absorption energy with respect to the values typical for tile cluster passivated only by hydrogen, while the emission energy appears to be influenced mainly b y the incorporated oxygen content. There is a Stokes shift reaching th e significant value of about 0.7 eV. It reduces with the increase of t he oxygen content down to a value of 0.2 eV in the case of OH-group-te rminated clusters, while it is almost constant for the oxygen-incorpor ated ones.