Mechanical properties of single crystals of silicon

Abstract

Single crystals of silicon were subjected to tensile tests in the temperature range from −196°c to 1380°c, with rate of straining 0.02, 0.20 and 1.00 min⁻¹. It was established that above 600°c crystals can be plastically deformed. At temperatures above 1100°c they can be strained up to 30%. The extent of strain at the ultimate tensile strength is independent of rate of straining and temperature. The phenomenon of upper and lower yield stress depends on the presence of oxygen in silicon. Dislocation-free crystals show a very large drop of the yield stress. This indicates that Cottrell's theory is not applicable to these crystals of silicon. It is postulated that in single crystals of silicon, small cracks on the surface of the sample are responsible for the observed fracture stresses. In some instances extremely high stresses were observed. They were smaller only by a factor of three than the theoretical yield strength. These experiments suggest that small cracks are the prevailing sources of dislocations in crystals of silicon.