Electrical and optical properties of as-deposited V2O5 –TeO2 amorphous films and their annealing effect

Abstract

DC electrical conductivity of vanadium–tellurite films both as-deposited by vacuum deposition and annealed at 773 K for 3 h after deposition are investigated in the temperature range of 323–473 K. All as-deposited films (250–350 nm thickness) show an amorphous structure; the annealed films show some crystalline peaks of TeO2. The conductivity of the as-deposited films at 373 K varies from 1.07 × 10–7 to 3.73 × 10–15 Scm–1. With annealing the conductivity increases by a factor of 10 to 103 due to the presence of some nanocrystals of TeO2 and also increases with an increase of the V2O5 content. The temperature dependence of the conductivity of both as-deposited and annealed films obeys a non-adiabatic small polaron hopping conduction mechanism. Seebeck coefficient measurements indicate all the films to be n-type semiconductors. From absorption edge analysis it is revealed that the optical band gap energy for the films is 2.96 eV and 3.11 eV for as-deposited films. Urbach tail analysis gives the width of localized states as 0.272 eV and 0.392 eV for two as-deposited films.