Elemental tin (Sn) undergoes a number of phase transitions that can change its electronic properties. For example, “alpha-tin” (α-Sn) is a zero-gap semiconductor exhibiting a variety of topologically nontrivial phases. Aside from fundamental interest in understanding the details of topological electronic states, there is widespread hope that unique functionalities in next-generation electronic devices can be based on such states.
However, α-Sn is unstable and goes through a phase transition to a trivial metal phase, β-Sn, at room temperature. In the past, a few approaches have been developed aimed at stabilizing it at higher temperatures. The most promising dealt with growing the films on substrates with closely matching lattices, such as indium antimonide (InSb), at room temperature.
“The resulting α-Sn films, however, contained indium impurities,” said Alexei Fedorov, a staff scientist at the Advanced Light Source (ALS) and a co-author of this study. “As result, the properties of the alpha-tin essential to novel electronics applications were severely altered.”
In this work, researchers demonstrated how an InSb substrate can be treated in such a way as to produce an increased concentration of Sb on the surface. A number of techniques were employed: angle-resolved photoemission spectroscopy (ARPES) at Advanced Light Source (ALS) Beamline 10.0.1 and at Stanford Synchrotron Radiation Lightsource (SSRL), molecular-beam epitaxy (for sample growth), scanning-tunneling microscopy, and magnetotransport studies.
The results showed that modification of the InSb substrate so that its surface is enriched with Sb prevents diffusion of In impurities into the α-Sn. Not only did the results show that an Sb-rich surface promotes growth of α-Sn, but the α-Sn may be grown at a wider-than-expected range of temperatures above room temperature. The latter is important in connection with the fabrication of future devices since some technological processes may need to be run at elevated temperatures. The reduction in indium concentration allows for the study of α-Sn electronic structure via ARPES without the need for bulk doping or surface dosing, simplifying topological phase identification.
The study is an important contribution to the quest for new but “viable” materials capable of replacing silicon, as it indicates that after some “fine tuning,” epitaxial growth of thin films—a technique widely used in microelectronics—can be used for manufacturing high quality, near intrinsic α-Sn.
A.N. Engel, C.P. Dempsey, H.S. Inbar, J.T. Dong, S. Nishihaya, Y. Chang, A.V. Fedorov, M. Hashimoto, D. Lu, and C.J. Palmstrøm, “Growth and characterization of α-Sn thin films on In- and Sb-rich reconstructions of InSb(001),” Phys. Rev. Mater. 8, 044202 (2024), doi:10.1103/PhysRevMaterials.8.044202.