Phase‐Pure α‐Sn Quantum Material on Si Seeded by a 2 nm‐Thick Ge Layer

Abstract α‐Sn, a new elemental topological quantum material, has drawn substantial attention lately. Unique transport properties and intriguing spintronics applications of α‐Sn are demonstrated, resurrecting this material from its notorious “tin pest” infamy. With a diamond cubic crystal structure, group‐IV α‐Sn holds the potential for integrated topological quantum devices on Si. However, directly growing α‐Sn on Si is still challenging due to the ≈20% lattice mismatch. Here, a new method is demonstrated to grow 200 nm‐thick α‐Sn microstructures on a 2 nm‐thick Ge seed layer on Si substrate by physical vapor deposition. In situ Raman spectroscopy reveals that the as‐deposited β‐Sn melts upon rapid thermal annealing at 350–450 °C and solidifies to α‐Sn after cooling back to room temperature, seeded by heterogeneous nucleation on the Ge layer. Cooling condition and HCl etching are tuned to achieve phase‐pure α‐Sn microstructures toward quantum devices. Approximately 1 at.% Ge is alloyed into α‐Sn due to diffusion from the Ge seed layer, which helps stabilize α‐Sn thermodynamically to facilitate device processing. A compressive strain is incorporated into these α‐Sn microstructures, making them 3D topological Dirac semimetals for integrated quantum devices on Si.