Investigation of structural, optical, electrical, thermoelectric and optoelectronic properties of undoped ZnO, Sb-doped ZnO and Sb–B co-doped ZnO thin films

Abstract

Pure ZnO (Zinc oxide), 1 % Sb (antimony) doped ZnO (Zn0.99Sb0.01O), and 1 % Sb–1% B (boron) co-doped ZnO (Zn0.98Sb0.01B0.01O) solutions were prepared using the sol-gel method. These solutions were deposited as thin films on glass and Si (silicon) substrates via dip coating and spraying methods. In this study, doping ZnO with low amounts of Sb and B provided the conversion of the n-type semiconductor ZnO into a p-type semiconductor. The produced thin films were pure and had wurtzite ZnO polycrystalline structure. The nanodot morphology of ZnO turned into a mixture of nanodot and nanorod structures with only Sb doping. Moreover, the band gap energy of ZnO decreased from 3.26 eV to 3.24 eV with Sb doping and to 3.23 eV with Sb and B co-doping, accompanied by a decrease in optical transmittance depending on film thickness. All samples exhibited diode characteristics. According to the created Au/ZnO–Zn0.99Sb0.01O – Zn0.98Sb0.01B0.01O/Si diodes, it was understood that the ideality factor, barrier height, and serial resistance of ZnO material decreased with doping. Especially, the ideality factor, barrier height, and serial resistance of the ZnO sample decreased from 4.95, 6.80 eV, and 1.42 × 105Ω to 4.35, 6.25 eV, and 2.60 × 103Ω, respectively, with Sb and B co-doping. The photovoltaic performance of 1 % Sb-doped thin film increased 100 times compared to pure ZnO, reaching the efficiency from 0.006 to 0.600. However, the most suitable material for use as a photodiode was found to be the 1 % Sb–1% B co-doped sample. While the leakage current of this sample is around −8.0 × 10−5 A at −3 V under 100 mW/cm2 light, it is 9.5 × 10−8 A at −3 V in the dark. Furthermore, the 1 % Sb-doped thin film exhibited the best performance as a thermoelectric material at 600 K, achieving a figure of merit (ZT) of 0.00052. Overall, co-doping with Sb and B enhanced the optical, electrical, and structural (more homogeneous and less surface roughness) properties of ZnO, while improving its optoelectronic functionality such as photodiode. On the other hand, thermoelectric and solar cell properties of ZnO were enhanced with only 1 % Sb doping. A hybrid energy system containing thermoelectric and solar cells was produced cheaply and simply for wide application areas with this study. Moreover, with such a low doping amount, p-type material production was achieved, and important physical properties of the ZnO material were improved.