Evidence of the Superposition of Drude Type and Hopping Type Transport in Boron-Rich Solids

Abstract

The dielectric function of the boron-rich solids in the FIR range is analyzed on the basis of their optical reflectivity spectra, which exhibit obviously typical, strongly increasing slopes with decreasing frequencies. It is shown that these slopes can be quantitatively described, when a superposition of Drude type and hopping type parts for the dynamical conductivity is assumed. The corresponding fits were simultaneously made for the real and imaginary parts of the dielectric function to achieve unambiguous parameters. The obtained results are consistent, e.g., with the DC conductivity of these semiconductors, and in particular in the case ofβ-rhombohedral boron with the known energy band scheme and the related electronic properties. The bipolaron hopping model of the electronic transport in boron carbide turns out to be inappropriate.