Defects and impurities in SiGe: The effect of alloying

As a fully miscible solid solution, silicon-germanium (Si1−xGex) alloy has attracted significant interest in recent years owing to its manifold applications in microelectronic and optoelectronic devices raised by the possibility of tailoring the band gap and lattice parameter. These additional degrees of freedom and the random distribution of Si and Ge atoms imply new phenomena not observed in elemental group-IV semiconductors. A fundamental understanding of the microscopic properties of the alloy is therefore essential for a good control of SiGe-based device performance. As a corollary, an ultimate understanding of the electronic properties of the most abundant point defects and impurities is needed. This review aims at describing recent results obtained with metallic impurities and irradiation-induced interstitial defects in strain relaxed Si1−xGex alloy in which two main aspects will be highlighted. Firstly, the electronic transitions between deep levels and the allowed bands as a function of Ge composition will be discussed with a special emphasis on practical consequences of the alloy-induced energy shifts. Secondly, the role of the atomic environment on the electronic transitions and diffusion mechanism will be highlighted.