The Effect of Charged Impurities on the Yield Point of Silicon

Dislocation‐free silicon single crystals heavily doped with phosphorus and boron are dynamically deformed in compression at high temperatures. Doping in the extrinsic region affects the yield point of silicon in two different ways: At high strain rates the activation energy of dislocation velocity as measured by the lower yield stress is decreased by phosphorus but is not changed by boron. At low strain rates marked deviations from this behaviour are observed. The lower yield stress becomes independent of strain rate, but still depends exponentially on deformation temperature and linearly on doping concentration. These results are interpreted on the basis of a strong short‐range electrostatic interaction between charged dislocations and oppositely charged solute atoms leading to impurity clouds around the dislocations.