First-principles simulations of a-Si and a-Si:H surfaces

We use ab initio local-density-approximation methods to develop an ab initio model of an a-Si and an a-Si:H surface. Starting with a supercell of bulk a-Si, we remove periodic boundary conditions in one direction and relax the sample using ab initio methods. H is added to remove bulk defects. The surface structure and coordination of atoms is discussed, and defect states are characterized. H is added to dangling bonds on the a-Si:H surface, creating a hydrogen-terminated a-Si:H surface. We explore the relationship between electronic and geometric surface defects.