Effects of morphology on the electrical and optical properties of thin bismuth films

Thin films of bismuth were evaporated onto polished Si(100) substrates at substrate growth temperatures which varied between 25 and 100° C. The variations in film morphology observed using the scanning electron microscope and atomic force microscope were compared to changes in the optical and electrical properties of the thin Bi films. The optical properties could be modeled using an effective medium approximation, which suggested that the roughness of the films changed with substrate growth temperature. The film roughness appeared to decrease with substrate temperature from room temperature deposition to a minimum roughness at temperatures of ∼70 °C. Higher temperatures again resulted in an increased roughness, which correlated with a change in morphology observed by SEM. The electrical resistance of the samples was not sensitive to roughness changes in the film, but did change abruptly for the higher temperature samples where the morphology was substantially different. The transverse magnetoresistance was sensitive to film structure, increasing with substrate growth temperature up to a maximum substrate temperature of 70 °C before decreasing again at higher temperatures.