Epitaxial growth of bismuth films and bismuth-antimony heterostructures

We describe an approach for fabricating high-quality Bi thin films and heterostructures on ${\mathrm{BaF}}_2$ substrates by epitaxially growing them between layers of semiconducting ${\mathrm{Bi}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sb}}_{\mathit{x}}$. We present results from reflection high-energy electron diffraction, scanning electron microscopy, and atomic force microscopy analysis and show that the films are single crystalline with typical rms roughness of 1 nm and a dislocation density of 2×${10}^9$ ${\mathrm{cm}}^{\mathrm{-}2}$. Low-temperature magnetoresistance measurements are discussed in detail for a 90-nm ${\mathrm{Bi}}_{0.95}$ ${\mathrm{Sb}}_{0.05}$/45-nm Bi/65-nm ${\mathrm{Bi}}_{0.95}$ ${\mathrm{Sb}}_{0.05}$ heterostructure. At liquid-helium temperatures, the electrical transport in the central, 45-nm-thick Bi layer is well described by a three-carrier model that takes into account high mobility electrons (${\mathrm{\mu }}_1$=1.0×${10}^5$ ${\mathrm{cm}}^2$/V s) and holes (ν=3.1×${10}^4$ ${\mathrm{cm}}^2$/V s), as well as low mobility surface charges. The electron and hole densities are roughly equal and a factor of 6 higher than in the bulk. The epitaxial growth and clean interfaces result in a long electron elastic-scattering length, ${\mathit{l}}_{\mathrm{el}}$=0.38 μm. From an analysis of the observed Shubnikov–de Haas oscillations we obtain values for the extremal cross section of the Fermi surface, the cyclotron mass, and the single-particle relaxation time. At 45 nm the film thickness is comparable to the Fermi wavelength and, due to quantum confinement, only a few two-dimensional subbands of the electron pocket are filled.