Defects induced by irradiation with fast neutrons in n-type germanium

Abstract

Electrically active defects induced in n-type Sb-doped Ge crystals by irradiation with fast neutrons have been studied by means of conventional deep level transient spectroscopy (DLTS). The neutron-irradiation-induced DLTS spectra are compared with those recorded after irradiations with 4 MeV electrons. The evolution of the neutron- and electron-radiation-induced defects upon 30-min isochronal annealing in the temperature range 100–300 °C has been investigated. Although the DLTS spectra from electron- and neutron-irradiated materials show some similarities and there are also significant differences. The neutron irradiation resulted in the appearance of a number of peaks related to electron and hole deep level traps in the DLTS spectra. In the upper half of the gap at least six electron traps were observed with the following activation energies for electron emission ( E n): 0.08, 0.12, 0.17, 0.22, 0.29 and 0.34 eV. Some of these traps were detected in the electron-irradiated samples. Particularly the trap with E n=0.34 eV was the dominant one after electron irradiation and was identified as the second acceptor level of the Sb–vacancy pair. In Ge:Sb samples irradiated with high fluences of neutrons the trap with E n=0.29 eV [ E(0.29)] was the dominant electron trap. It is argued that the E(0.29) trap is related mainly to the second acceptor level of Ge divacancy (V 2). It is suggested that upon annealing of neutron-irradiated samples at temperatures higher than 100 °C mobile divacancies and Sb–V pairs can interact with Sb atoms with the formation of Sb–V 2 and Sb 2–V complexes, which have acceptor levels in the lower half of the gap.