Oxygen impurity states in an amorphous silicon matrix

The electronic structure of an oxygen impurity atom in an amorphous silicon ($a$-Si) matrix has been investigated. The theoretical calculations, using a first-principles method of orthogonalized linear combinations of atomic orbitals, are based on a series of realistic structural models in which the oxygen atom appears as: (1) a bridging, (2) a nonbridging, (3) a bridging with a hydrogen atom bonded to a Si atom, or (4) a nonbridging hydrogen-compensated impurity center. Results are presented for the local density of states of O, H, and the Si atoms to which they bond. No gap states are found for all cases considered, indicating O may be a very effective healing element for structural defects in $a$-Si. It is further concluded that an H atom is more likely to bond to an Si atom than to an O atom.