Theory of Vibrations of Pairs of Defects in Silicon

Abstract

The theoretical⁽¹⁾⁽²⁾ and experimental study⁽³⁾⁽⁴⁾ of the vibrations of defects in silicon has been developed in the last years. Localised modes have been observed by infrared optical absorption when a light charged boron impurity is introduced. To remove the free carrier absorption a lithium⁽⁴⁾ or phosphorus⁽³⁾ donnor impurity has to be added. Some of the absorption bands can be explained as due to isolated boron impurities and agree with a simple mass defect model⁽²⁾. The other bands appearing with sufficiently high impurity concentrations^(5)(6)(7) can only be explained with a model of pair defects. Two different pair defect configurations have been identified, a pair of substitutional impurities and a pair of one substitutional and one interstitial impurity. The theory of these pair defects have been recently made⁽⁸⁾ using a Green’s function technique and is extended to calculate the frequency and the intensity of the observed localized mode absorption bands.