Structural, Electrical and Optical Properties of ZnO Thin Films Co-doped with Titanium and Hydrogen Prepared by RF Magnetron Sputtering with Different Substrate Temperatures

Abstract

Transparent conducting oxides (TCOs) exhibit a distinctive blend of exceptional transparency and electronic conductivity, making them pivotal in diverse optoelectronic devices. Among these, indium tin oxide is widely used, while zinc oxide (ZnO) emerges as a promising TCO material with substantial commercial applications. This research endeavors to enhance the optoelectronic characteristics of titanium and hydrogen co-doped ZnO (TZO:H) thin films by manipulating the substrate temperature during deposition and introducing hydrogen gas. TZO:H thin films were fabricated on glass substrates via radio-frequency magnetron sputtering, utilizing a sputtering target composed of 1.5 wt% TiO₂-doped ZnO. Varied H₂/(Ar+H₂) flow ratios (R_H = 0–15%) and substrate temperatures (T_S = RT–300°C) were employed. The structural, electrical, and optical properties of the TZO:H thin films were thoroughly examined through X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall-effect measurements, UV/Visible/IR spectrophotometry, and X-ray photoelectron spectroscopy. XRD analysis revealed that all TZO:H films exhibited a hexagonal wurtzite structure with a predominant (002) orientation. The average transmittance in the visible region exhibited a decline with increasing R_H in RT-deposited films, whereas it remained relatively stable at different R_H levels for films deposited at 300°C. The resistivity of TZO:H films exhibited a strong dependence on both T_S and R_H. Through optimization of substrate temperature and hydrogen flow rate, the minimum resistivity of the TZO:H thin film experienced a notable reduction by over two orders of magnitude to 9´10^-4 \(\Omega\)×cm.