Ge1-Xsnx Alloys: Consequences Of Band Mixing Effects For The Evolution Of The Band Gap Gamma-Character With Sn Concentration

In this 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 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, in contrast to the sharp indirect-to-direct band gap transition obtained in conventional alloys such as Al1-xGaxAs. Understanding the band mixing effects is critical not only from a fundamental and basic properties viewpoint but also for designing photonic devices with enhanced capabilities utilizing GeSn and related material systems.