Physical properties of amorphous boron films deposited by pyrolysis of decaborane

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 77K to 1000K. It is found that the electrical conductivity varies from 3 x 10-5 at 77K to 30S.cm-1 at 1000K. The activation energy is 1.07 eV over the intrinsic temperature range (700 -- 1000K). Thermo-electric power is positive over the temperature range investgated from 500 K to 1000 K and the maximum value is about 420 μV.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 μm and reaches minimum at 12.5 μm, which is attributed to be presence of short range order in the lattice. (author)