Fluctuations and correlations in sputtering and defect generation in collision cascades in Si

This paper concerns the investigation of certain statistical properties of collision cascades in a Si target, induced by Ge ions in the energy range 1 -200 keV. The first and second moments, i.e. the mean and the variance of t he number of defects and the sputter yield were calculated as functions of the projectile energy. Two-point correlation functions of the defect depth distribution and temporal correlations in sputtering have also been calcula ted. Such investigations have been made in the past mostly for amorphous ma terials. In this paper both amorphous and crystalline structures are invest igated. All calculations were made by the binary collision code MARLOWE. Th e effect of the crystalline structure on the calculated statistical quantit ies of the cascade, in particular the effect of channelling, can be studied quantitatively. It was found that for crystalline structures the energy de pendence of the relative variance of the defect number and the sputter yiel d, as well as the structure of the two-point correlations, follow similar t rends as those in an amorphous solid. The magnitude of the relative varianc e can be both higher and lower for the crystalline material as compared to the amorphous one, depending on the bombarding angle, projectile energy, an d the type of quantity considered (defects or sputtering). On the whole, th e fluctuations appear to be larger in the crystalline material. (C) 2000 El sevier Science B.V. All rights reserved.