Effects of vacancy defects on the mechanical properties in neutron irradiated Czochralski silicon

Abstract

We have investigated the mechanical properties of neutron irradiated Czochralski (NICZ) silicon using nanoindentations combined with micro-Raman spectroscopy. It is found that NICZ silicon shows higher hardness (∼13% higher) than non-irradiated silicon, with a slightly lower Young’s modulus. When the samples were subjected to isochronal anneals in the temperature range of 250 °C–650 °C, the hardness of NICZ silicon gradually decreases as the temperature increases and it is finally comparable to that of the non-irradiated silicon. The vacancies and vacancy–oxygen defects induced by neutron irradiation in NICZ silicon annihilate or transform into more complex defects during the annealing processes. It suggests that the vacancy defects play a role in the evolution of hardness, which promote phase transition from the Si-I phase to the stiffer Si-II phase in NICZ silicon during indentation. In addition, the irradiation induced vacancy defects could lead to the lower Young’s modulus.