Defect Dynamics and the Properties of Amorphous Silicon – a New Perspective

Abstract

In the last twenty years, the dominant paramagnetic defect in a-Si (the D center) was believed to be threefold-coordinated Si (dangling bond) which is not mobile. Many observations, however, have not been explained in a satisfactory way. This paper summarizes recent contributions of the present author which offer a novel and systematic description of the properties of a-Si. It is shown that overcoordinazion is an essential concept and that fivefold- and threefold-coordinated Si are the primitive conjugate intrinsic defects. Overcoordination is the key to defect migration and thus to the realization of reactions between intrinsic defects, hydrogen, and impurities. Most properties of a-Si are a consequence of a small set of reactions. The available data favor the identification of the D center as fivefold-coordinated Si (floating bond). Dangling bonds are nonmagnetic and their signature is a photoluminescence peak at ∼0.9 eV.