Low-temperature electrical-transport properties of single-crystal bismuth films under pressure

Abstract

We report an investigation of the low-temperature electrical transport properties of bismuth films under applied hydrostatic pressure. Films with their trigonal axis perpendicular to the film plane and thicknesses of 30, 50, and 500 nm were grown by molecular-beam epitaxy on ${\mathrm{BaF}}_{2}$ substrates. At 500 nm thickness the behavior resembles that of bulk Bi. From the observed Shubnikov--de Haas oscillations we find a pressure-induced decrease in extremal Fermi cross section. For the 30-nm film, we obtain the low-temperature carrier densities for electrons and holes together with the corresponding mobilities from magnetoconductance data at pressures up to 20 kbar. We find that pressure strongly reduces the surface-induced excess hole concentration, clearly revealing a finite electron concentration at high pressures. We discuss our results within the context of a possible semimetal-semiconductor transition in thin Bi films. \textcopyright{} 1996 The American Physical Society.