Optical and Electrical Properties of Boron

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 ω was found to follow the equation α= B (ω- E 0 ) 2 /ω and constants E 0 and B were 1.00 eV and 1.7∼2.1 × 10 5 cm -1 ·eV -1 respectively. High temperature conductivity σ of amorphous boron was expressed in the form σ= C exp (- E / k T ) and 2 E and C were 1.04∼1.16 eV and 7∼12 × 10 3 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.