Vacancies and interstitial atoms in e−-irradiated germanium

Abstract

High purity Ge wafers have been irradiated at low temperatures with MeV electrons and have subsequently been investigated by x-ray diffraction methods. The intensity of the Huang diffuse scattering shows that a high concentration of defects (>1019 cm−3) can be frozen in at 4 K. A large fraction of the defects is stabilized in the form of close Frenkel pairs which are characterized by the nearly perfect cancellation of the long range displacement fields of the interstitial atom and the vacancy. We discuss the absolute size of these displacements as well as the introduction rate of the defects, which is of the order of ∑=3 cm−1. The high defect introduction rates are at variance to the results of electrical and optical investigations and indicate that these methods detect only a few percent of the total defect concentration which is produced and frozen in at 4 K. The consequences for the understanding of the defect production in Ge and for the assumption of an athermal migration of interstitial atoms are discussed in close relation to similar results for Si. In addition, we discuss the differences between the defect patterns observed after 4 K irradiation to those observed after room-temperature irradiations and the thermally activated defect reactions up to the final annealing at 600 K.