Electrical characterization of MeV heavy-ion-induced damage in silicon: Evidence for defect migration and clustering

We have studied electrical activity of defects created by high-dose MeV heavy-ion implantation in $n$ -silicon. Heavy damage induced by ${\mathrm{Ar}}^{\mathrm{+}}$ and ${\mathrm{Au}}^{\mathrm{+}}$ ions is embedded within depletion layers of Schottky diodes. The defects are characterized using capacitance–voltage $\mathrm{(C–V),}$ current–voltage $\mathrm{(I–V),}$ deep-level transient spectroscopy (DLTS) and time analyzed transient spectroscopy techniques. Large concentration of defects in the depletion layer of as-implanted device lead to unusual features in $\mathrm{C–V}$ and $\mathrm{I–V}$ characteristics. The damage layer is found to extend several microns beyond the ion range or the damage profile predicted by standard Monte Carlo simulation packages. The dominance of a single trap in the damaged region is established from hysteresis effect in $\mathrm{C–V,}$ space-charge-limited conduction in forward $\mathrm{I–V}$ and DLTS spectrum. With annealing in the temperature range of $\text{400–600\hspace{0.17em}°}\mathrm{C},$ the observed changes in the defect profile indicate that the effective electrical interface between damaged and undamaged layer moves progressively towards the surface. From transient spectroscopic analysis the major defect is found to be a midgap trap whose energy is sensitive to the degree of disorder in the damaged layer. The experimental features in $\mathrm{C–V}$ characteristics have been simulated using model charge profiles taking into account crossing of the Fermi level with the midgap trap within the depletion layer. The simulations suggest the presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence, in qualitative agreement with recent predictions of molecular dynamics simulations, of defect migration and clustering of interstitial related defects even at room temperature in the case of high-dose irradiation.