Ge1-xSnx alloys: Consequences of band mixing effects for the evolution of the band gap Γ-character with Sn concentration

<p>In this&nbsp;work we study the nature of the band gap in GeSn alloys for use in silicon-based lasers. Special attention is paid to Sn-induced band mixing effects. We&nbsp;demonstrate from both experiment and ab-initio theory that the (direct) &Gamma;-character of the GeSn band gap changes continuously with alloy composition and has significant &Gamma;-character even at low (6%) Sn concentrations. The evolution of the &Gamma;-character is due to Sn-induced conduction band mixing effects,&nbsp;in contrast to the&nbsp;sharp indirect-to-direct band gap transition obtained in conventional alloys such as Al_1-xGa_xAs. Understanding the band mixing effects is critical not only from a fundamental and basic properties&nbsp;viewpointbut also for designing photonic devices with enhanced capabilities utilizing GeSn and related material systems.</p>