Novel Growth of Phase-Pure α-Sn Quantum Microstructures on Si Using a Ge Seed Layer

The elemental topological quantum material α-Sn has recently gained significant attention for its unique transport properties and potential spintronics applications [1]. Overcoming the notorious "tin pest" instability, α-Sn with its diamond cubic structure offers promising integration possibilities for topological quantum devices on Si. However, direct growth on Si is challenged by a significant lattice mismatch. Growths of α-Sn on Si were reported, but the thickness was limited to below 10 nm [2].<br/><br/>In this study, we introduce a novel method to grow 200 nm-thick α-Sn microstructures with lateral dimensions reaching 0.4-1 μm on a Si substrate by employing a 2 nm-thick Ge seed layer via physical vapor deposition [3]. Up to 86% of as-deposited β-Sn converts to α-Sn under optimal thermal annealing conditions, which significantly enhances the phase purity compared to ~50% α-Sn in our previous work of Ge-doped α-Sn grown on native oxide on Si [4]. Cooling process is found to be critical to α-Sn formation. Using in situ Raman spectroscopy, we confirm that as-deposited β-Sn melts during rapid thermal annealing (RTA) at 350-450°C and solidifies into α-Sn upon cooling, facilitated by heterogeneous nucleation on the Ge layer. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) reveal single-grain α-Sn microdots with identical crystallographic orientation within each microdot. Approximately 1 at.% Ge diffuses into the α-Sn, aiding thermodynamic stabilization and processing. Tuning cooling conditions and employing HCl etching, we further achieve phase-pure α-Sn microstructures suitable for quantum device applications. This α-Sn incorporates a compressive strain of ~-0.59%, induced by the Ge seed layer, confirming its nature as a 3D topological Dirac semimetal compatible with Si-based quantum devices [5]. Our discoveries provide a platform for several potential applications, including exploring point-contact induced superconductivity [6], investigating transport properties [7], and studying optical modulation [8]. Our method’s compatibility with CMOS technology presents a significant advancement toward quantum materials integration on Si and opens up opportunities for practical applications in quantum electronics and spintronics. Future work will explore a broader range of Ge seed layer thicknesses and epitaxial growth of Ge seed layer on Si substrate to further optimize the α-Sn growth process and device integration.<br/><br/>Reference<br/>[1] Si, N. <i>et al.</i> <i>J. Phys. Chem. Lett.</i> <b>2020</b>, <i>11</i>, 1317–1329.<br/>[2] Ding, J. <i>et al.</i> <i>Adv. Mater.</i> <b>2021</b>, <i>33</i>, 1–9.<br/>[3] Liu, S. <i>et al.</i> <i>Small Methods</i> <b>2024</b>, 2400550.<br/>[4] Liu, S. <i>et al.</i> <i>Commun. Mater.</i> <b>2022</b>, <i>3</i>, 17.<br/>[5] Anh, L. D. <i>et al.</i> <i>Adv. Mater.</i> <b>2021</b>, <i>33</i>, 2104645.<br/>[6] Aggarwal, L. <i>et al.</i> <i>Nat. Mater.</i> <b>2016</b>, <i>15</i>, 32–37.<br/>[7] Ding, Y. <i>et al.</i> <i>arXiv: 2308.02192</i> <b>2023</b>.<br/>[8] Li, W. <i>et al.</i> <i>Nano Lett.</i> <b>2014</b>, <i>14</i>, 955–959.