Epitaxial bismuth telluride layers grown on [111] barium fluoride substrates suitable for MQW-growth

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Abstract
Multi quantum wells and superlattices are discussed as suitable tools for increasing ZT. Best layer quality should be expected only for lattice matched growth. Therefore [111] barium fluoride should be most suitable compared to other common substrates like mica and sapphire, although up to now epitaxial growth of bismuth telluride on [111] barium fluoride with atomically flatness was not achieved. We present the first bismuth telluride-layers reproducibly prepared on [111] barium fluoride substrates using the molecular beam technique. Three essential factors influence the growth of bismuth telluride on barium fluoride: substrate temperature, the flux ratio of Bi/Te and substrate surface preparation itself even for single crystal [111] barium fluoride substrates. These dependencies of growth characteristics and layer properties are reported. AFM and RHEED analysis show suitable layer by layer growth of bismuth telluride with step height of 1 nm as expected from its crystal structure. Step widths of growth terraces are similar to those known from other MQW-suitable systems like IV-VI-compounds. Further X-ray analysis combined with EDX-analysis (single crystals standard) indicates single phase growth with stable stochiometric composition.

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