Silicon samples of initial oxygen concentration [O 17 cm -3 were subjected to various high temperature-high pressure (HT-HP) treatments in the temperature range 900-1050 °C. Afterwards, the samples were irradiated by fast neutrons and then isothermally annealed at 400 °C. Infrared spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), optical spectroscopy and selective etching measurements were performed. Besides the precipitates and the dislocation loops that usually form, small defect clusters were also detected in the samples. The presence of these clusters is revealed due to their decoration with radiation induced point defects, and attributed to the HP treatment
