Charge carriers and morphology of thin film Bi(111) grown on mica and on Si(111)

Carriers in Bi and Bi(111) surfaces possess electronic and spin properties that render them compelling for the study of new quantum states of matter and topological systems. Strong spin-orbit interaction exists in the Bi(111) surface electron states and hyperfine interaction usefully couples electron and nuclear spin systems [1]. High-quality thin films are indicated to use the quantum properties of Bi(111) but the growth is challenging, given the aim to approach the carrier qualities of pure single-crystals. Bi films can also undergo a semimetal to semiconductor transition due to the formation of a quantum-confinement energy gap. We deposited Bi(111) films of thickness 10, 20, 40 or 60 nm on mica (van der Waals epitaxy) [1] and on Si(111)7x7 (Stranski-Krastanov epitaxy) and performed detailed magnetotransport measurements over 4-296 K. A 3-carrier model including metallic electrons in surface states and electrons and holes in the films' interiors provided densities, mobilities and mean-free paths of the 3 carrier types, and provided estimates of the quantum-confinement energy gap. A higher overall crystalline quality of van der Waals epitaxy on mica is evidenced by superior electronic transport properties compared to growth on Si(111), as will be discussed.