Extended point defects in crystalline materials: Ge and Si

TL;DR

This paper investigates the nature of self-interstitial point defects in germanium and silicon, revealing two forms with different entropies and proposing a new defect structure called a 'morph' that influences diffusion.

Contribution

It introduces the concept of 'morphs' as amorphous-like defect structures in crystalline materials, supported by experimental diffusion data and computational modeling.

Findings

Two distinct self-interstitial forms identified in Ge.

High-temperature diffusion dominated by complex 'morph' defects.

Computational models suggest morphs exist in multiple defect types.

Abstract

B diffusion measurements are used to probe the basic nature of self-interstitial 'point' defects in Ge. We find two distinct self-interstitial forms - a simple one with low entropy and a complex one with entropy ~30 k at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket - we name it a 'morph'. Computational modelling suggests that morphs exist in both self-interstitial and vacancy-like forms, and are crucial for diffusion and defect dynamics in Ge, Si and probably many other crystalline solids.