Fabrication of Al doped ZnO films using atmospheric pressure cold plasma

Abstract

Under atmospheric pressure, homogeneous non-equilibrium cold plasma was generated stably by high voltage pulsed power (1kV, 20kHz, 38W) excitation of a mixture of He and O2 gases produced by a dielectric barrier discharge setup. By feeding Bis (2 methoxy‐6-methyl‐3, 5-heptanedione) Zn (Zn-MOPD, C18H3O6Zn) and Tris (2-methoxy‐6‐methy l‐3, 5-heptanedione) Al (Al-MOPD, C27H45O9Al) into this plasma with He carrier gas, transparent flat Al-doped ZnO (ZnO:Al) films about 120–240nm thick were prepared on glass substrates directly under the slit made into the cathode. Deposition rates of the films were about 20–40nm/min. The concentration of Al was measured by inductively coupled plasma atomic emission spectroscopy. The composition ratio of Al to Zn was 7.8mol% when the carrier He gas flow rate of Al-MOPD was 30cm3. The average transmittance of all films was more than 85% in the wavelength range from 400 to 800nm. When the composition ratio of Al/Zn was between 1.1 and 7.8mol%, the optical band gap of the film increased from 3.28 to 3.40eV. The resistivity of ZnO:Al film was 2.96Ωcm at 1.3mol% of Al/Zn. In addition, the microstructure of the films was studied by X-ray diffraction measurement and field emission scanning electron microscope observation. It was revealed that doped Al is substituted onto the Zn site of the ZnO crystalline structure in ZnO:Al films.