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

Abstract

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 Zn 1− x Cd x O and Zn 1− y Mg y O alloy films, have been deposited by this mist-CVD system. The films deposited at the temperatures ranging from 400 to 500 °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 1.08×10 –3 Ω 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 Ω cm, Hall mobility of 2.28 cm 2 V −1 s −1, and hole concentration of 3.76×10 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 Zn 1− x Cd x O and Zn 1− y Mg y O ternary alloys were also deposited by this technique. The band gap energies, for instance, were 3.05 eV for Zn 1− x Cd x O ( x=0.06), 3.28 eV for ZnO, and 3.56 eV for Zn 1− y Mg y O ( 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.