EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Tin can exist under two different crystalline structures. α-Sn is a cubic crystal and is stable below 13°C. On the other side, β-Sn has the tetragonal phase and is stable above 13°C. In terms of electronic properties, α-Sn is a semimetal and was predicted to possess various topological phases. Moreover, β-Sn is a superconductor with a critical temperature of 3.74K. Interestingly, α-Sn is lattice matched with InSb. Recent works on epitaxial growth of thin films on InSb showed that α-Sn films can be stabilised above the transition temperature. We also demonstrated that β-Sn thin films deposited on InSb nanowires induce hard superconducting gaps with superconductivity persisting up to 4T. For those reasons, the Sn-InSb system is a great platform to study topological transport phenomena. Yet, controlling the formation and the stability of the different tin phases on InSb is challenging.
In this context, we fabricated Sn thin films on InSb substrates with different crystalline orientations at temperatures as low as 85K (-188°C). Such low deposition temperatures ensure the wetting of the metallic layer on the InSb substrate, allowing for the formation of ultra-thin films. We deposited Sn films InSb substrates with thicknesses ranging from 6 to 40 nm. The thin films were characterised by X-ray diffraction and low temperature transport measurements. All samples show epitaxial relationship between α-Sn and InSb. Out-of-plane XRD reveal that the extracted thickness of the α-Sn film is slightly thinner than the nominal deposited thickness. When switching to in-plane XRD geometry, we observe the presence of β-Sn grains in the deposited film. Their presence is responsible for the superconductivity of the thin film appearing at low temperature. Further studies will clarify the relationship between the structural and electronic properties of the Sn thin films as well as the influence of the film thickness on those properties.