Divacancy clustering in neutron-irradiated and annealedn-type germanium

Abstract

We have studied the annealing of vacancy defects in neutron-irradiated germanium. After irradiation, the Sb-doped samples ͓͑Sb͒ = 1.5ϫ 10 15 cm −3 ͔ were annealed at 473, 673, and 773 K for 30 min. The positron lifetime was measured as a function of temperature ͑30-295 K͒. A lifetime component of 330 ps with no temperature dependence is observed in as-irradiated samples, identified as the positron lifetime in a neutral divacancy and indicating that the divacancy is stable at room temperature ͑RT͒. Annealing at 673 K resulted in an increase in the average positron lifetime, and in addition, the annealed samples further showed a larger lifetime component of 430 ps at RT, which is due to larger vacancy clusters. The average positron lifetime in the samples annealed at 473 K has a definite temperature dependence, suggesting that the divacancies become negative as the crystal recovers and the Fermi level moves upwards in the band gap. Annealing at 673 K, reduces the average lifetime and intensity of the defect component 2 at RT, indicating that the vacancy clusters have started to anneal. Negative divacancies are still present in the samples after this anneal. Annealing at 773 K is enough to remove all observable vacancy defects.

Direct observations of the vacancy and its annealing in germanium

“…Furthermore, strong evidence of a negative charge state for the divacancy in the bandgap was also reported. 28 These findings are supported by a recent DLTS study by Petersen et al 29 A few low-temperature irradiation PAS studies on germanium have previously been reported. [30][31][32] A common feature of all these studies is that electron irradiation has been performed at cryogenic temperatures, and the samples have then been transported and measured at liquid nitrogen temperatures.…”

“…28. As the average lifetime at RT in the sample used in this study is considerably lower as compared with that of Ref.…”

Evolution of vacancy-related defects upon annealing of ion-implanted germanium

“…There are very few quantitative PAS studies done in germanium and to make a more exact estimate of the cluster size is therefore difficult. However, a qualitative estimate can be made by using the present results in conjunction with the recent result for the Ge divacancy 15 and by comparing with similar studies in silicon. 10 Hakala et al found an approximately linear relation between the normalized S parameter and the cluster size.…”

Total Dose and Dose Rate Effects on Some Current Semiconducting Devices

“…Fewer results were published concerning highpurity germanium detectors for which early efforts were significant. Published results seems to show that annealing is not complete, although radiation induced point defects anneal out around 200°C (Mooney et al,1983; , clusters and other extended defects remain in the bulk of the crystal and only disappear at higher temperatures (Kuitunen et al,2008). Other materials are used for semiconductor detectors, but have not attracted so much interest in terms of radiation tolerance.…”