Physical Properties of Amorphous Boron Films Deposited by Pyrolysis of Decaborane

Abstract

Electrical and optical properties of amorphous boron films deposited by pyorolysis of decaborane at the pressure of molecular flow region have been studied.
Electrical conductivity was measured in the temperature range from 77 K to 1000 K. It is found that the electrical conductivity varies from 3 x 10^-5 S·cm^-1 at 77 K to 30 S·cm^-1 at 1000 K. The activation energy is 1.07 eV over the intrinsic temperature range (700-4000 K). Thermoelectric power is positive over the temperature range investgated from 500 K to 1000 K and the maximum value is about 420μV·deg^-1 at 700 K.
Absorption coefficient, refractive index and extinction coefficient of the boron films were calculated from the measured values of the transmittance and reflectance. The energy gap of indirect allowed transition was estimated to be 1.28± 0.08 eV. In the infrared spectral region the transmittance decreases steeply at about 8 pm and reaches minimum at 12.5 μm, which is attributed to be presence of short range order in the lattice.