Energies and structural properties of hydrogen and related defects in molecular-dynamics-modeleda-Si:H

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Abstract
We use ab initio pseudopotential local-density-approximation methods to create and study related supercells containing 62 Si atoms and from 5 to 7 H atoms. In particular, we obtain energies and structural properties of H in different charge states that are passivating dangling bonds, in bond-centered positions, and in other interstitial sites. The most striking result found is the rather large (of order 1 eV) spread of energies for a given type of defect, depending on its surroundings. We also find that changes in single-particle energies or energy eigenvalues from defect to defect are not particular close to changes in the total energy and that the distinction, between bond-centered H and a dangling bond plus a Si-H bond, is not as clear cut as one might think. The calculations also provide insights into possible migration mechanisms and energies for H movement.