Compositional tuning in sputter-grown highly-oriented Bi-Te films and their optical and electronic structures.

Growth of Bi-Te films by helicon-wave magnetron sputtering is systematically explored using alloy targets. The film compositions obtained are found to strongly depend on both the sputtering and antenna-coil powers. The obtainable film compositions range from Bi55 Te45 to Bi43 Te57 when a Bi2 Te3 alloy target is used, and from Bi42 Te58 to Bi40 Te60 (Bi2 Te3 ) for a Te-rich Bi30 Te70 target. All films show strong orientation of the van der Waals layers (00l planes) parallel to the substrate. The atomic level stacking of Bi2 Te3 quintuple and Bi bi-layers has been directly observed by high resolution transmission electron microscopy. Band structure simulations reveal that Bi-rich Bi4 Te3 bulk is a zero band gap semimetal with a Dirac cone at the Gamma point when spin-orbit coupling is included. Optical measurements also confirm that the material has a zero band gap. The tunability of the composition and the topological insulating properties of the layers will enable the use of these materials for future electronics applications on an industrial scale.