Hopping transport in evaporated polycrystalline tellurium films

Abstract

Abstract Polycrystalline tellurium films with thicknesses in the range 100–1300 nm were prepared by thermal evaporation onto glass substrates. The d.c. electrical conductivity was measured in the temperature range 77–400 K. The electrical conductivity σ was found to increase both with increasing thickness and on annealing. The activation energy estimated from Arrhenius plots shows a strong temperature dependence in unannealed and annealed films of various thicknesses. A critical examination of the temperature-dependent activation energy indicates the inadequacy of the relation σ ∝ exp (- T 0 T ) 1 4 which is often used to explain the d.c. conductivity of tellurium films in the temperature range 77–170 K. The dependence of σ on T can be adequately explained by a model which incorporates the temperature-dependent overlap of electron wavefunctions and predicts σ ∝ 1 T exp (AT) The constant A gave a reasonable value of the electron wavefunction decay constant (α-1 ≈ 0.1 nm) by assuming a phonon frequency ω of about 1013 Hz in annealed and unannealed tellurium films of various thicknesses.