Reversed Phase Transformation of β→α-Sn at Elevated Temperatures towards Quantum Material Integration on Silicon

Abstract

α-Sn and SnGe alloys have recently attracted much attention as a new family of topological quantum materials. However, bulk α-Sn is thermodynamically stable only at <13°C. Moreover, scalable integration of α-Sn quantum materials/devices on Si has been hindered by a large lattice mismatch. To address these challenges, we demonstrate compressively strained α-Sn doped with 2-4 at.% Ge on a native oxide layer on Si, grown at 300-500°C through a reversed β-to-α-Sn phase transformation without relying on epitaxy. The size of α-Sn microdots reaches up to 200 nm, ~10x larger than the upper size limit for α-Sn formation reported before. Furthermore, the compressive strain makes it one of the few candidates for 3D topological Dirac semimetals with interesting applications in spintronics. We find that Ge-rich GeSn nanoclusters in the as-deposited materials seeded the reversed β-to-α-Sn transition at elevated temperatures. This process can be further optimized for SnGe quantum material and device integration on Si.