ZnO-based thin films synthesized by atmospheric pressure mist chemical vapor deposition

An atmospheric pressure mist chemical vapor deposition (mist-CVD) system has been developed to prepare zinc oxide (ZnO)-based thin films. This is a promising method for large-area deposition at low temperatures taking into account of its simplicity, inexpensiveness, and safety. Nominally pure ZnO, Al-doped n-type ZnO (ZnO:Al), and N-doped p-type ZnO (ZnO:N) thin films, as well as Zn1-xCdxO and Zn1-yMgyO alloy films, have been deposited by this mist-CVD system. The films deposited at the temperatures ranging from 400 to 500 degrees C were of an acceptable crystallinity with (0 0 2) preferential orientation and homogeneous surface. All the films exhibited high transmittance of about 90% in visible regions and dominant UV emission in the photoluminescence spectra. The n-type ZnO:Al films had a low resistivity of 1.08 X 10(-3) Omega cm at an optimal Al content of 4 at%. The p-type conductivity was obtained in ZnO:N films annealed at higher temperatures with a resistivity of 72.8 Omega cm, Hall mobility of 2.28cm(2)V(-1)s(-1), and hole concentration of 3.76 x 10(16)cm(-3), as confirmed by Hall-effect measurements. A hydrogen-assisted nitrogen-doping mechanism was proposed to answer for the realization of p-type conductivity in ZnO. The films of Zn1-xCdxO and Zn1-yMgyO ternary alloys were also deposited by this technique. The band gap energies, for instance, were 3.05eV for Zn1-xCdxO (x = 0.06), 3.28eV for ZnO, and 3.56eV for Zn1-yMgyO (y = 0.11), as confirmed by the optical absorption spectra. The band gap engineering could be readily realized in the ZnO system using mist-CVD. (c) 2006 Elsevier B.V. All rights reserved.