Energy spikes in Si and Ge due to heavy ion bombardment

Abstract

The number of displaced atoms/ion, N∗_D , produced by heavy ion bombardment (10-250 keV) of Si and Ge at 35 K is reported. A semi-empirical formulation is given, based upon the separation of the damage into a “spike” component and a “collisional” component, which adequately predicts N∗_D , for all ions and energies investigated. The “spike” concept is also tested by investigation of damage enhancement effects occuring for diatomic bombardment with equal atom dose and equal energy/atom corresponding to the monatomic bombardments. The semiempirical model is found to adequately predict the diatomic damage enhancement for heavy ions, e.g. Te+₂, but shows discrepancies for lower mass ions. The reasons for such discrepancies are discussed. For Si targets, the “spike” component appears to fit a thermal-spike model, whereas for Ge it is suggested that a damage-spike (localized lattice collapse within the individual cascade) better interprets the experimental results. Spike diameters, D_S, for various ions and energies are determined and found to be consistent with T.E.M. observed amorphous zones.