Defects in Irradiated Silicon. II. Infrared Absorption of the Si-ACenter

The Si-A center is a major, radiation-damage defect produced in "pulled" silicon by room temperature irradiation. In this paper (II), we present the infrared measurements which, in conjunction with the spin resonance measurements of the preceding paper (I), establish the identity of the Si-A center. A new infrared absorption band is observed at 12 in electron-irradiated silicon. This band is shown to be a vibrational band of impurity oxygen in the lattice. Macroscopic and microscopic correlations between the 12- band and the spin resonance of the Si-A center are presented. The macroscopic correlations are of production rate, recovery, etc. The microscopic correlations derive from the absorption of polarized infrared radiation by samples of various crystallographic orientations, subjected to a uniaxial, compressive stress. Partial alignment of the defects is induced by the stress and is detected as a dichroism in the 12- band. This alignment is compared to the corresponding alignment studies in the spin resonance measurements in Paper I. It is shown that the kinetics and magnitude of the response to the stress are the same for the defects observed in both types of measurements. This shows that the 12- band arises from the Si-A center and established the configuration of the oxygen in the defect. These results, together with the results of Paper I, allow us to conclude that the Si-A center is a lattice vacancy with an oxygen atom bridging two of the four broken bonds associated with the vacancy. The remaining two bonds can trap an electron, giving rise to the spin resonance spectrum of the defect. The identification of the Si-A center indicates that the vacancy is mobile in a room temperature irradiation.