Aerosol assisted chemical vapour deposition of Ga-doped ZnO films for energy efficient glazing: Effects of doping concentration on the film growth behaviour and opto-electronic properties
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High quality Ga-doped ZnO thin films for use as energy efficient glazing coatings were deposited onto glass substrates by low cost single source aerosol assisted chemical vapour deposition (AACVD) of zinc and gallium acetylacetonates (in methanol) at a temperature of 350 °C. The effect of Ga content ranging from 0.4 at% to 6.1 at% on the structural and functional properties of ZnO films was investigated. Highly c-axis oriented films are easily formed in the case of pure ZnO with hexagonal (002) surfaces observed. This texture is gradually weakened in 0.4 at% to 3.0 at% Ga doped samples, and the deposit morphology is transformed to granular particles, irregular platelets, agglomerated particles and wedge-like structures, respectively, which may result from retarded grain boundary growth and increasing exposed non-(002) surfaces. Further gallium addition to 4.3 at% suppresses the grain growth and deteriorates the system crystallinity, with a concomitant change to a (102) preferential orientation in the heavily 6.1 at% Ga doped sample. The ZnO:Ga coatings exhibit high carrier concentration (up to 4.22 × 10<sup>20</sup> cm<sup>-3</sup>) and limited carrier mobility (<5 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup>), and the minimum resistivity value obtained is 1.16 × 10<sup>-2</sup> Ω cm. Due to their large band gaps (3.14-3.42 eV) and favourable carrier numbers, high visible transmittance (83.4-85.3%) and infrared reflection (up to 48.9% at 2500 nm) are observed in these films, which is one of the best AACVD ZnO reported for low emissivity application and close to the optical requirements for commercial energy saving glazing.