Optical studies of ion-implantation centres in silicon

Photoluminescence enables a very large number of defects to be observed in ion-implanted silicon, over dose ranges of up to at least 10¹⁴ cm^-2. Simple arguments using the widths of the luminescence lines suggest that the defects lie in the heavily damaged part of the implanted crystal. We show that by combining optical absorption measurements on neutron-irradiated samples with luminescence measurements on implanted samples, the relative concentrations of ion-implantation defects may be determined. The luminescence spectra are shown to change considerably with temperature over the limited range 10-40 K. In this temperature range, the total number of photons emitted by the layer is conserved, further implying that the strengths of the signals from each defect are proportional to the concentrations of those defects. Some luminescence lines can be linked to DLTS signals, allowing the high resolution capabilities of luminescence to be combined with the ability of DLTS to measure concentrations, providing powerful joint probes into the properties of the implanted regions.