The Optical and Electrical Constants of Beta-Rhombohedral Boron

Abstract

Reflectivity data obtained from two samples of beta-rhombohedral boron were used to calculate the optical properties in the wavelength range 0.45–0.65 μ. One sample was composed of very small crystallites; the other was mono-crystalline. The absorption coefficients were approx. 10⁵ cm^-1 and are attributed to direct optical transitions from the valence band to the conduction band. The absorption threshold energy E _T of the monocrystalline sample was calculated to be 1.26 ± 0.04 eV, which is in agreement with the value for the thermal activation energy Eg of 1.27 ± 0. 01 eV obtained by Brungs for the same sample. The index of refraction of both samples was 3 and the dielectric constant 11 in the wavelength range 0.45–0.65 μ. These data are in agreement with the values obtained by Spitzer, Morita, and Lagrenaudie. The extinction coefficient of the polycrystalline sample varies from 1 at λ = 0.45 μ to 0.6 at λ = 0.65 μ; for the monocrystalline sample, the extinction coefficient varies from 0.65 to 0.35 over the same wavelength region.