Energy spikes in Si and Ge due to heavy ion bombardment

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, DS, for various ions and energies are determined and found to be consistent with T.E.M. observed amorphous zones.