We tried to study the effect of the in-situ hydrogen post-treatment on undoped ZnO thin films grown on heated Corning 7059 glass by Photo-MOCVD method. Thus, ZnO thin films have been prepared by four different methods at a low temperature of 140℃ using diethylzinc(DEZ) and $H_2O$ as reactant gases. The following methods were used; MOCVD method, MOCVD and in-situ hydrogen post-treatment method, Photo-MOCVD method, and Photo-MOCVD and is-situ hydrogen post-treatment method. The thickness of all the films was 1.4㎛. During the film growth, UV light irradiation effectively improved the electrical and optical properties. Moreover, the optical bandgap of the film dramatically widened by 0.15eV.
The in-situ hydrogen post-treatment with the UV irradiation of the undoped ZnO thin films by MOCVD dramatically enhanced the electrical and optical properties. The resistivity of an 20-minute $H_2$-treated film improved from 8.13Ω cm to $1.24×10^{-2} Ω cm$, the haze ratio increased from 4.19% to 7.07%, and no degradation of total transmittance was observed.
The in-situ hydrogen post-treatment with the UV irradiation of the undoped ZnO thin films by Photo-MOCVD slightly enhanced the electrical and optical properties. The resistivity of an 20-minute $H_2$-treated film improved from $7.88×10^{-4} Ω cm$ to $7.31×10^{-4}Ω cm$, the haze ratio increased from 7.92% to 10.3%, and no degradation of total transmittance was observed. This is the lowest resistivity so far reported for undoped ZnO thin films by Photo-MOCVD method. The enhanced resistivity may be caused by the oxygen desorption effect, which must be supported by the UV light and mercury-sensitized hydrogen atoms.
Highly transparent and conductive ZnO:Al thin films were successfully grown on Corning 7059 glass substrates by Photo-MOCVD technique at a low temperature of 140℃ using diethylzinc(DEZ) and $H_2O$ as reactant gases. We used the vapor from the aqueous solution of aluminum chloride hydrate($AlCl_3(6H_2O)$) solution as the doping gas. It was found that Al doping has an important role in grain growth and surface morphology. The haze ratio increased from 7.92% to 10.3% and no degradation of total transmittance was observed. Al was also used to improve the electrical properties, acting as an N type dopant. The low resistivity ZnO:Al thin film with the resistivity of $6.77×10^{-4}Ωcm$ was obtained. This is the lowest resistivity so far reported for ZnO thin films by MOCVD or Photo-MOCVD method. $AlCl_3(6H_2O)$ is very inexpensive and can be obtained with ease. Moreover, it is not toxic. Therefore, this new method is very economical as well as stable.
