Ch Park

First-principles study of the optical properties of SiC

Abstract We examine the optical properties of SiC in the 3C, 2H, 4H, and 6H structures through first-principles pseudopotential calculations. The dielectric response function in the optical limit exhibits anisotropic behaviour for the hexagonal polytypes, which arises from hexagonal crystal fields. In the 6H structure, we find that the density of states near the conduction band edge is rapidly increasing and the optical response is significantly enhanced in the ultraviolet energy region. Such peculiar behaviour in the density of states and the dielectric response lead us to understand that 6H SiC is a more promising material for optical devices, compared with other polytypes.

Atomic model for hydrogen passivation of DX centers in GaAs and AlxGa1−xAs alloys

Abstract We present the atomic model for the hydrogen passivation of DX centers in GaAs and Al x Ga 1−x As alloys doped with Si and S donors using an ab initio pseudopotential method. In GaAs, the DX centers with the negative- U property are found to be stabilized at pressures above 22 kbar. Both the shallow donors and deep DX centers are neutralized by hydrogen via the formation of donor-hydrogen complexes which are neutral in a charge state. In Al x Ga 1−x As alloys, we study the effects of the Al atoms on the interactions between H and its neighboring atoms. The calculated dissociation energies for the donor-hydrogen complexes agree with measured values.