In situX-ray topographic study of the dislocation mobility in high-purity and impurity-doped silicon crystals

Abstract

An in situ X-ray topographic technique using a high-power X-ray generator has been used to study the dislocation mobility at elevated temperatures in the stress range 1·2-40 MN m⁻² for pure and impurity-doped silicon crystals. The variation of velocity with stress for both 60° and screw dislocations in high-purity crystal is linear throughout the whole stress range investigated, the activation energies for motion being independent of stress. No previously published theoretical models are able to account for the measured velocities quantitatively. Effects of impurities, such as oxygen, carbon, nitrogen, phosphorus and boron, are investigated in detail. Generally, the impurities bring about a deviation from linearity of the variation of velocity with stress under low stresses. Dislocations originally moving in impure crystals are immobilized when the stress becomes lower than a critical value. These phenomena are interpreted in terms of the development of an impurity atmosphere around slowly moving dislocations. Phosphorus atoms are known to enhance the dislocation motion under high stresses and to retard it under low stresses.