EPITAXIAL-GROWTH OF BISMUTH-FILMS AND BISMUTH-ANTIMONY HETEROSTRUCTURES

We describe an approach for fabricating high-quality Bi thin films and heterostructures on BaF2 substrates by epitaxially growing them between layers of semiconducting Bi1-xSbx. 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 2X10(9) cm(-2). Low-temperature magnetoresistance measurements are discussed in detail for a 90-nm Bi0.95Sb0.05/45-nm Bi/65-nm Bi0.95Sb0.05 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 (mu(1)=1.0 X 10(5) cm(2)/V s) and holes (nu = 3.1 X 10(4) 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, l(el) = 0.38 mu m. 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.