Electrical and optical properties of Cr2O3 films prepared by chemical vapour deposition

Polycrystalline Cr2O3 films are prepared by normal pressure chemical vapour deposition (CVD), and electrical and optical properties of the films are investigated. The films are transparent from 800 to 1000 nm wavelength, and absorbing for wavelengths shorter than 800 nm. The optical band gap energy is E(opt) = 2.98 to 3.09 eV for films formed at different substrate temperatures. The electrical conductivity sigma of the films is from 1 x 10(-2) to 2.5 x 10(-3) S cm(-1) at 500 K. The films are p-type semiconducting. At temperatures higher than 500 K, the conduction is due to small polaron hopping. For temperatures lower than 500 K, a T--1/4 dependence of sigma T-1/2 is found, which is attributed to variable-range hopping.