Effect of rapid thermal treatment on the electrical conductivity improvement of nc-ZnO:Bi thin film and ITO substrate

Abstract

Spherical nano crystalline zinc oxide doped with bismuth (nc-ZnO:Bi) spin-coated on indium tin oxide (ITO) substrates exhibited the improvement of conductivity under the rapid thermal annealing (RTA) treatment. The ZnO:Bi nanostructure was formed at 550 °C annealing temperature, which severely affect the ITO electrical quality and closely relevant with the device performance. The efficiency of relevant electronic devices has been limited by the low electrical conductivity of the transparent electrodes. RTA treatment in the ambient atmosphere condition was applied to ZnO:Bi film coated on ITO substrate to perform the good spherical nc-ZnO:Bi properties and to persist in the ITO low resistivity, concomitantly which results in significant improvement of electrical and optical properties of nc-ZnO:Bi/ITO substrate. RTA process was subjected at varying temperature conditions from 700 °C to 930 °C for 20 s. It is noticeable that the RTA can obtain ZnO:Bi nanostructure, good optical property, and high ITO conductivity existence, simultaneously. The nano-spherical ZnO:Bi around 10–20nm diameter size at the film surface morphology provides the reflectance of 6%, and the transmittance of above 90% at 930 °C RTA for 20 s. The photocurrent of nc-ZnO:Bi/ITO films provides between 10−2 to 1 A/cm2 at 0.5 V. The RTA process can improve electrical property of ITO films with uniform distribution of oxygen vacancy. Surface morphology and crystalline grain quality of the thin film were investigated after RTA treatment. In addition, optical absorbance and energy gap (Eg) of nc-ZnO:Bi/ITO substrate evaluated by Tauc plot is a crucial attribute to apply in a promising photonic device. Thus, the high electrical and optical qualities of such nc-ZnO:Bi/ITO films can be used to produce an electron transport layer for organic solar cells and transparent contact electrodes for low-cost semiconductor devices.