Termination-dependent surface properties in the giant-Rashba semiconductorsBiTeX(X=Cl, Br, I)

Sebastian Fiedler,Oleg E Tereshchenko,Matthias Bode,Hendrik Bentmann,Friedrich Reinert,Sergey V Eremeev,Konstantin A Kokh,Evgueni V Chulkov,Thomas Bathon,Paolo Sessi

doi:10.1103/physrevb.92.235430

Abstract

The noncentrosymmetric semiconductors $\mathrm{BiTe}X\phantom{\rule{4pt}{0ex}}(X=\text{Cl},\text{Br},\text{I})$ show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single-crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), and density functional theory calculations to systematically investigate the structural and electronic properties of $\mathrm{BiTe}X(0001)$ surfaces. For $X=\text{Cl}$, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.

Highlights

The narrow-gap semiconductors BiTeX (X = Cl,Br,I) have attracted considerable interest because of large Rashba-type spin-orbit splittings in their bulk and surface electronic structures [1,2,3], which have been observed by angle-resolved photoelectron spectroscopy (ARPES) [4,5,6,7,8] and magnetotransport measurements [9,10]
A possible explanation for this behavior could be the similar atomic radii of the first layer (Te) and I atoms, that might be expected to promote the formation of mixed Te/I layers during the crystal growth
Our density functional theory (DFT) calculations indicate that the formation energy for stacking faults in the bulk is much smaller for BiTeI (1 meV) than for BiTeBr (46 meV) and BiTeCl (60 meV), in line with the experimental findings

Summary

Introduction

The enhanced spin splitting in these materials is driven by their noncentrosymmetric crystal structure in combination with strong atomic spin-orbit coupling and a negative crystal-field splitting of the topmost valence bands [11]. The latter features have been predicted to promote a topological insulator phase in BiTeI under application of external pressure [12]. The BiTeX series does host the presently largest known Rashba effect of all semiconductors; it appears more suitable for possible spin-electronic applications [13,14] than artificially grown monolayer reconstructions, such as metallic surface alloys, where spin splittings of similar magnitude can be achieved [15,16,17,18]. The surface properties may be influenced by defects, as is the case for BiTeI, where bulk stacking faults induce coexisting Te- and

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Results

Discussion

Conclusion