Influence of precursor type, deposition time and doping concentration on the morphological, electrical and optical properties of ZnO and ZnO:Al thin films grown by ultrasonic spray pyrolysis

• Zn acetate resulted in considerably better conductivity.
• Increasing deposition time increased the surface roughness.
• Al doping improved the conductivity without affecting the optical transparency.
• Films grown using Zn nitrate exhibited considerably better photoconductivity.

The influence of precursor type, deposition time and doping concentration on the morphological, optical and electrical characteristics of ZnO and ZnO:Al thin films and nanostructures deposited by ultrasonic spray pyrolysis at 400 °C on glass substrates was investigated. A deposition period of 30 min resulted in compact, uniform samples with thickness of 30 and 45 nm, and growth rates in the order of 1 and 1.5 nm/min for the Zn acetate and Zn nitrate precursors, respectively. The as-grown films showed good adhesion and excellent optical transmission. Moreover, films grown using Zn acetate precursor exhibited considerably low resistivity, being 14 Ω·cm for a deposition time of 30 min. Surface roughness was observed to increase with deposition time, while Al doping up to 5% reduced the resistivity down to 4 Ω·cm without affecting the optical transmission of the films. Finally, films grown using Zn nitrate were observed to exhibit better photoconductivity than those grown with Zn acetate.