Structure of Deuteron-Irradiated Germanium

Abstract

The structure of deuteron-irradiated germanium is discussed in the light of the following recent experiments: (1) simultaneous measurements of the change in length and resistivity upon low temperature bombardment and annealing, (2) measurement of lattice parameter changes after annealing near room temperature, and (3) low-angle x-ray scattering measurements at liquid nitrogen temperature and above. A model of the damage at liquid nitrogen temperature consisting of separated clusters of vacancies and interstitials, is proposed. The model yields a comparatively small length increase and fairly strong low-angle x-ray scattering in agreement with experiment. The model also appears capable of explaining the experimental observation that resistivity annealing occurs in an earlier stage of the recovery process than appreciable length-change annealing. The clusters must be formed, at or below liquid nitrogen temperature, either by diffusive motion of the defects or by displacement processes directly upon bombardment. If the latter mechanism holds, present theory greatly underestimates displacement distances in germanium. Additional critical experiments are proposed.