Electrical conductivity and optical properties of ZnO films annealed in hydrogen atmosphere after chemical vapor deposition

The d.c. electrical conductivity and optical properties of polycrystalline zinc oxide films (220-450 nm thick) annealed in hydrogen after chemical vap or deposition are investigated. A minimum film resistivity after the anneal ing gives 0.31 Omega cm for the film as-deposited at a substrate temperatur e of 823 K. From the temperature dependence of conductivity, band conductio n is confirmed for the films at temperatures above 250 K. The effect of gra in-boundary scattering is due to thermionic emission of electrons over grai n boundary barriers. At temperatures below 250 K, variable-range hopping tr ansport is found to be dominant. The films are transparent in the wavelengt h range 400 to 1000 nm and have sharp ultraviolet absorption edges at 380 n m. The absorption edge analysis reveals the optical band gap energy for the films to be 3.18-3.23 eV. The Urbach tail analysis gives the width of loca lized states E-e=0.06-0.14eV. (C) 2001 Kluwer Academic Publishers.