Sol-gel production of p-type ZnO thin film by using sodium doping

• Investigated sol-gel deposited ZnO:Na using NaOH.
• Stable p-type ZnO can be obtained by Na doping above 2 at.%.
• The structure and optical properties of ZnO:Na is degraded as a function of Na doping.
• A pn junction was constructed using p-type ZnO:Na/ZnO on indium doped tin oxide coated glass substrate.

In this study, ZnO:Na thin films doped with 1–5 at.% of Na were synthesized on glass substrates by the sol-gel deposition technique. The morphology and optoelectronic properties of the thin films were characterized by using the environmental scanning electron microscope (SEM), X-ray diffraction (XRD), UV–Vis spectroscopy and Hall effect measurements. The SEM images and XRD pattern both indicated a substantial change in the film structure as the Na content increases due to the oversupply of the OH− ions in the initial precursor solution. UV–Vis spectroscopy measurements revealed that the increase in Na doping resulted in the decreases of the optical transmittance and the optical band gap due to the formation recombination centers. Hall effect measurements confirmed that the ZnO:Na films doped with >2 at.% of Na are stable with p-type conduction behaviour. As a demonstration, a ZnO-based junction was fabricated using the synthesized ZnO:Na/ZnO thin films on indium tin oxide glass substrates.

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