SiGe nanowires: Structural stability, quantum confinement, and electronic properties

We report first-principles calculations of [110] SiGe NWs; we discuss the effect of geometry and composition on their thermodynamic stability, on their electronic properties, and on the nature of the quantum confinement effect. The analysis of formation enthalpy reveals that Ge-core/Si-shell NWs represent the most stable structure at any diameter, as a confirmation of the results of many experimental works. The study of the dependence of the energy band gap on the composition and geometry shows how abrupt NWs (wires with a clear flat interface between Si and Ge) present strongly reduced quantum confinement effect and offer a very easy way to predict and to engine energy band gap, which can have a strong relevance from a technological point of view. A careful analysis of the influence of composition on the wave-function localization and quantum confinement effect is also presented, in particular, for core-shell NWs.