Energy-dependent amorphization of Ge by Ne, Ar or Kr on irradiation

Thin Ge specimens have been irradiated at room temperature with Ne, Ar or Kr ions of different energies, and the doses required for complete amorphization determined by in situ transmission electron microscopy and electron diffraction. Onset of amorphization was detected after the lowest ion doses, reflecting amorphization by individual ions. The ion dose required for complete amorphization increased nearly linearly with ion energy over the range 0.5-3.5 MeV for all ions. Amorphization cross-sections have been determined for all the ions and energies used. The amount of damage, expressed as the number of displacements per atom, required for complete amorphization decreased with increasing ion energy or ion mass. The decrease with increasing ion energy or ion mass is due to a decrease in irradiation-enhanced annealing of amorphous volumes as a result of a decrease in the fraction of low-energy atomic displacements to Ge. Increasing the fraction of low-energy atomic displacements to Ge atoms during Kr irradiation by simultaneous 1 MeV electron irradiation increased the Kr ion dose required for complete amorphization. Radiation annealing is believed to be due to freely migrating defects produced by low-energy atomic displacements to Ge atoms. (Author)