Simulation of Semiconductor Nanostructures

We employ density functional and quantum Monte Carlo calculations to show that significant changes occur in the optical gap of fully hydrogenated nanoclusters when the surface contains impurity passivants such as atomic oxygen. Our results show that quantum confinement is only one mechanism responsible for visible photoluminescence in silicon nanoclusters and that the specific surface chemistry must be taken into account in order to interpret experimental results. In the case of oxygen, the gap reduction computed as a function of the nanocluster size provides a consistent interpretation of several recent experiments. Furthermore, we predict that other double bonded groups also significantly affect the optical gap while single bonded groups have a minimal influence.