Extended point defects in crystalline materials: Ge and Si

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

Overlayer stress effects on defect formation in Si and Ge

International audiencePoint-defect formation energies in bulk crystalline materials such as Si and Ge are material specific quantities defined for the case of formation at a free surface, but in many cases of technological interest, point defects are formed at the interface between the crystalline substrate and a strained material overlayer. Here the energy cost of generating a bulk point defect at the overlayer/substrate interface is modified by the stress interaction during defect formation, leading to an effective supersaturation or undersaturation in the bulk, relative to the 'equilibrium' concentration expected for the case of a free surface. This in turn impacts on diffusion, defect formation and activation of dopant impurities in the substrate. We present current experimental evidence for this phenomenon, based on studies of B diffusion under tensile-strained nitride layers, and discuss the likely implications for dopant activation in Si and Ge

TCAD simulation and development within the European DOTFIVE project on 500GHz SiGe:C HBT's

International audienceThe TCAD infrastructure developed within the DOTFIVE project is described. The hierarchical TCAD platform includes different Boltzmann equation solvers as well as simulators based on the widely used drift-diffusion and hydrodynamic transport models. In the latter case, accurate physical models were generated. The TCAD platform is used to explore the physics of extremely scaled devices and investigate new device concepts and architectures