Open-volume defect profiles were obtained by applying Doppler broadening methods, using a slow positron beam, to p-type samples which had been implanted with 20keV He ions to fluences of 5 x 1015 or 2 x 1016/cm2 at near liquid-N temperatures. The evolution of the defect profiles was studied as a function of isothermal annealing at 250C. The fraction of released He was measured by means of thermal programmed desorption. The defects could be characterized as being coexisting monovacancies which were stabilized by He-related defects and divacancies. The number of defects decreased for annealing times of a few minutes, and then increased at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very close to the surface. After annealing, the mean depth increased to less than half of the projected He range. The complex dynamics were interpreted as being due to the passivation of vacancies by He during implantation and initial annealing, where no appreciable He was lost, and to subsequent depassivation during He desorption.

He implantation-induced defects in Si studied by slow positron annihilation spectroscopy R.S.Brusa, G.P.Karwasz, N.Tiengo, A.Zecca, F.Corni, G.Calzolari, C.Nobili: Journal of Applied Physics, 1999, 85[4], 2390-7