molecular beam epitaxy and characterization of Bi₂Se₃ and Sb₂Te₃on In₂Se₃ layers via selenium passivation of non-vicinal InP(111)B substrates

Topological Insulators (TI) have gained much attention due to their non-trivial topology facilitating a wide variety of applications. However, there is a large unintentional background doping that conceals their surface channels, and crystal defects such as twin domains are frequently observed. Although these are van der Waals materials, the influence of the substrate on the molecular beam epitaxy (MBE) material properties has been shown to be non-negligible. Non-vicinal InP(111)B has been used before and reported by some to produce good material properties, yet it has been challenging to completely suppress the twin domains. In this study, we explore the quality of epitaxial Bi₂Se₃ and Sb₂Te₃ on 5 nm ultra-thin In₂Se₃ layers grown by a selenium passivation technique during the oxide desorption of the InP(111)B substrates, without the use of an indium source. AFM shows the formation of a smooth In₂Se₃ layer and the HR-XRD shows its high crystallinity, with the presence of satellite peaks from which the thickness could be extracted. Morphology of Bi₂Se₃ exhibits smooth surfaces with large terraces. AFM of Sb₂Te₃ show planes with steps, with a larger roughness than Bi₂Se_3. Φ scans of the (015) plane of both the Bi₂Se₃ and Sb₂Te₃ layers show complete suppression of twin domains. Further investigation showed that the direction of the twin suppression is sometimes parallel to the (311) plane of the InP(111)B substrates and other times it is in the opposite direction. In either case we observe full twin suppression.