Reduced twinning and surface roughness of Bi₂Se₃ and Bi₂Te₃ layers grown by molecular beam epitaxy on sapphire substrates Available to Purchase

The authors investigate the structural properties of Bi₂Se₃ and Bi₂Te₃ topological insulator layers grown on sapphire (0001) substrates by molecular beam epitaxy, using various pregrowth optimization methods. Samples of Bi₂Se₃ grown on sapphire with a particular combination of pregrowth surface treatment steps showed evidence of greatly reduced twinning and significantly reduced surface roughness. Evidence of twinning, and its suppression by the appropriate choice of pregrowth steps, is obtained from x-ray diffraction Φ-scan measurements as well as atomic force microscopy (AFM) images. Improved surface roughness is also evident from the AFM images. Growth of Bi₂Te₃ on sapphire exhibited similar reduced twinning by the application of the pregrowth surface preparation steps, although the surface roughness was significantly greater than that of Bi₂Se₃. Additional improvements in surface roughness of the Bi₂Te₃ were achieved by growing the Bi₂Te₃ on a Bi₂Se₃ buffer layer.