Investigation of defect structure of neutron-irradiated crystalline silicon by low-temperature thermal conductivity

The thermal conductivity of initially n-type silicon irradiated at temperatures higher than room temperature with fast neutron doses between 2·10¹⁸ and 2·10¹⁹ n/cm² and following thermal annealing at 375 °C and 800 °C was measured at low temperatures (2–200 K). Additionally, the heat capacity was investigated in the temperature range from 2 K to 50 K. With the help of the analysis of (T) on the basis of the Callaway model, results on the nature of neutron-induced defects and their change by annealing were obtained. The neutron-induced damage can be described by point defects and by extended defects in the kind of dislocations or dislocation loops, respectively. The interaction of point defects with phonons appears as Rayleigh scattering and partially as resonance-like scattering. At the Si sample with highest neutron dose, an anomalous behavior (cooling effect) was observed after annealing at 375 °C. The state of structure is not stable by cooling between room temperature and 78 K and therefore a decrese of (T) with each cooling cycle is obtained. A significant change of specific heat was not observed by neutron irradiation.