Studies of Far-Infrared Properties of Thin Bismuth Films on BaF₂Substrate

Abstract

The plasma frequencies (ω p ) of epitaxially grown bismuth film on BaF 2 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.