Complex Structures In Tetrahedrally Bonded Semiconductors

Complex tetrahedral structures form good models for amorphous Group IV and HI-V semiconductors. With a view of working towards examining non-crystalline materials, the structural, electronic and vibrational properties of complex tetrahedrally bonded semiconductors are investigated by various molecular dynamics techniques. First principles quantum mechanical molecular dynamics calculations are performed on two such structures and the effects of pressure on their behaviour is reported. A full free energy calculation using this method remains infeasible and therefore an empirical bond charge model is used to calculate the full pressure-temperature phase diagram of the structures. Several surface reconstructions of a complex phase of silicon are then examined and the lowest energy surface of any silicon structure so fax is found. Point defects in the diamond phase of silicon and carbon also give insight into various unusual bonding topologies that could be found in their amorphous phase. Structural and vibrational properties of several defects are considered. Finally, calculations on amorphous carbon and silicon at several densities are done and a comparison between the structural and electronic properties made. New bonding topologies are found in the structures including three centre bonding orbitals in the amorphous carbon models.