Effect of uniaxial stress on local vibrational modes of hydrogen in ion-implanted silicon

The interactions of hydrogen with intrinsic defects in proton-implanted silicon crystals have been studied by infrared absorption spectroscopy in conjunction with uniaxial stress. After implantation at room temperature numerous lines, associated with local vibrational Si-H stretching modes, have been revealed, in accordance with previous reports. The measurements have been carried out at low temperatures to reduce the linewidths. Only the lines observed at 1839, 1934, 2062, and 2166 cm^-1 have been investigated in detail. From the analysis of the stress-induced shifts and splittings of the lines, the symmetries of the relevant defect centers have been deduced. It has been found that the 1839-, 2062-, and 2166-cm^-1 lines originate from defects with trigonal symmetries, whereas the 1934-cm^-1 line corresponds to a monoclinic center of type I. The annealing behaviors of the lines have been determined and the results have been used to indicate whether different stretching modes are related to the same center. Moreover, from measurements on samples, where hydrogen atoms are partially substituted by deuterium atoms, some information about the number of hydrogen atoms involved in the various defects has been obtained. The 1839- and 2062-cm^-1 centers each involve a single Si-H bond. Detailed models for these two centers, consistent with the present observations and recent channeling experiments, are suggested. The 1934-cm^-1 line is tentatively assigned to a divacancy, having one or two dangling bonds saturated by hydrogen atoms. The 2166-cm^-1 line is ascribed to the activation of a twofold degenerate stretching mode, while another line at 2162 cm^-1, related to the same center, is believed to be associated with a nondegenerate mode. The 2166-cm^-1 center contains more than one hydrogen atom, and various models are briefly discussed.