Raman Spectroscopy for the Analysis οf Temperature-Dependent Plastic Relaxation οf SiGe Layers

Novel architectures for electronics and photonics are expected to be developed using the forthcoming $Si_{1-x}Ge_{x}$ technology. However, in $Si_{1-x}Ge_{x}$-based heterostructures, materials and design issues rely on accurate control of strain and composition of the alloy. The Raman spectroscopy has rapidly emerged as a reliable technique for the quantitative determination of such parameters on a sub-micrometric scale. In this work we present an investigation of the effects of the growth conditions of $Si_{1-x}Ge_{x}$ graded layers on dislocation nucleation and interaction. In particular, we focus on the crucial role the deposition temperature plays in the dislocation kinetics. The analysis of threading dislocation densities is accompanied by a quantitative measurement of the residual strain in $Si_{1-x}Ge_{x}$/Si heterostructures, carried out by means of the Raman scattering. Our approach is effective in studying the physical mechanism governing dislocation multiplication and the sharp transition from a state of brittleness to a state of ductility within a narrow temperature window.