Structural relaxation in amorphous silicon and the role of network defects

Abstract

Structural relaxation of amorphous Si (a-Si) can be viewed as either a general network rearrangement (short range ordering) or as the analogue in a-Si of defect annihilation processes in crystal Si (c-Si). Some recent experimental results are discussed in the light of these two alternatives. The annealing kinetics of ion bombardment damage in a-Si and c-Si are remarkably similar. The solubility of Cu in a-Si decreases with annealing, whereas the diffusivity increases which suggests removal of trapping sites (defects) from the material as relaxation proceeds. These phenomena can be understood when it is assumed that structural relaxation of a-Si is fully controlled by annihilation of point defects. The defect density in fully unrelaxed a-Si is estimated to correspond to several at.% displaced atoms. The absence of a measurable densification upon structural relaxation of a-Si suggests mutual annihilation of low-and high-density defects.