Studies of Far-Infrared Properties of Thin Bismuth Films on BaF₂ Substrate

Abstract

The plasma frequencies (ω_p) of epitaxially grown bismuth film on BaF₂ are determined from the far-infrared reflectivity as a function of film thickness (d). With decreasing d, ω_p increases at first and then decreases abruptly near d=100 A. This is considered as a sign of semimetal-semiconductor transition caused by the quantum size effect. The temperature dependences of ω_p and its damping factor are also measured with various d. The cyclotron mass of the electron band increases with decreasing d. To explain these experimental results, the strain effects of the film due to the lattice mismatch between the film and the substrate have to be taken into account.