Neutron-irradiation-induced defects in germanium: A Laplace deep level transient spectroscopy study

Deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and L-DLTS combined with uniaxial stress have been used in this work for characterization and identification of electrically active defects induced in Sb-doped germanium crystals by irradiation with fast neutrons. The samples were irradiated with relatively small doses of neutrons (≤5 × 10¹¹ cm⁻²) in order to produce uniformly distributed damage and to detect small defect clusters. It is found that for such low neutron doses in many respects the damage produced is similar to that resulting from electron irradiation. Vacancy-antimony (V-Sb) pairs uniformly distributed in the sample bulk are the dominant defects observed in the DLTS spectra. It is inferred from the L-DLTS measurements under application of uniaxial stress that the V-Sb pair has a trigonal symmetry in the doubly negatively charged state. It is argued that an electron trap with the activation energy for electron emission of 0.1 eV is related to an acceptor state of a small vacancy cluster located in highly damaged regions of the neutron-irradiated samples. L-DLTS measurements under application of uniaxial stress indicate that the symmetry of the defect is low, monoclinic-I, C_1h point group, or lower. Environment-induced broadening of the L-DLTS signal due to this centre prevents precise determination of the defect symmetry.