Optical and Electrical Properties of Boron

Abstract

Optical constants of β-rhombohedral and amorphous boron were obtained by ellipsometry and by the measurements of transmissivity and reflectivity. The values of the refractive index were found between 3.00 and 3.35 for wavelengths between 0.35 µm and 1.20 µm. Absorption coefficient α of amorphous boron as a function of the photon energy \hbarω was found to follow the equation α=B(\hbarω-E0)2/\hbarω and constants E0 and B were 1.00 eV and 1.7∼2.1×105 cm-1·eV-1 respectively. High temperature conductivity σ of amorphous boron was expressed in the form σ=C exp (-E/kT) and 2E and C were 1.04∼1.16 eV and 7∼12×103 ohm-1·cm-1 respectively. Absorption of β-rhombohedral boron was considered to be caused by indirect transitions from valence band to conduction band. From the temperature dependence of conductivity, the energy gap between valence band and conduction band was estimated to be 1.34 eV for β-rhombohedral boron.