Structural relaxation and defect annihilation in pure amorphous silicon.

Abstract

Thick amorphous Si layers have been prepared by MeV self-ion-implantation and the thermodynamic and structural properties examined by calorimetry, Raman-spectroscopy, and x-ray-diffraction techniques. Defects have been introduced into well-annealed amorphous and single-crystal Si by He, C, Si, and Ge bombardment. The defect structures are examined by these techniques and by transmission electron microscopy. The structure of amorphous Si in intermediate states of relaxation or annealing have been determined. It is shown that amorphous Si formed by either implantation or deposition contains a large population of point defects and point-defect clusters. Amorphous Si formed by laser quenching cannot be distinguished from well-annealed amorphous Si. Structural relaxation, also known as short-range ordering, can be understood as annihilation of a large fraction of these defects. Both structural relaxation in amorphous Si and defect annihilation in crystalline Si obey bimolecular reaction kinetics. The defect-formation and -annihilation processes are similar in amorphous and crystalline Si. Defect saturation occurs in amorphous Si at estimated defect concentrations of about 1 at. %. These formation and annihilation properties are intrinsic to pure amorphous Si. For hydrogenated amorphous Si, it is pointed out that the metastable-defect-creation and -annealing processes are essentially different from the annihilation processes in pure amorphous Si.