Increased photoluminescence of strain-reduced, high-Sn composition Ge1−<i>x</i>Sn<i>x</i> alloys grown by molecular beam epitaxy

Abstract

We synthesized up to Ge0.914Sn0.086 alloys on (100) GaAs/InyGa1−yAs buffer layers using molecular beam epitaxy. The buffer layers enable engineered control of strain in the Ge1−xSnx layers to reduce strain-related defects and precipitation. Samples grown under similar conditions show a monotonic increase in the integrated photoluminescence (PL) intensity as the Sn composition is increased, indicating changes in the bandstructure favorable for optoelectronics. We account for bandgap changes from strain and composition to determine a direct bandgap bowing parameter of b = 2.1 ± 0.1. According to our models, these are the first Ge1−xSnx samples that are both direct-bandgap and exhibit PL.