Uncharacteristic effect on the ultraviolet and visible photoluminescence properties of ZnO:Cl films: A physical insight

Study on the photoluminescence (PL) properties of cation or anion doped sol-gel ZnO thin films can lead to new insights into its defects. In this work, an in-depth knowledge on defect formation in phase pure Cl doped ZnO films has been acquired through comprehensive studies on their PL properties supported by the electrical and X-ray photoelectron spectroscopy (XPS) results. Here, we demonstrate an uncharacteristic enhancement in the ultraviolet (UV)/visible (VIS) peak intensity ratio from 2.7 to 9.5 with an increase in the doping content from 0–10 at% Cl, signifying a large change in the defect chemistry. Also an atypical change in the green (GE) and orange emission (OE) with a gradual decrease in the GE/OE intensity ratio as Cl dopant increases has been observed which is not reported earlier. Critical analyses of the UV and VIS PL emissions and electrical results supported by XPS data indicate that Cl occupies oxygen vacancy site forming Cl_O and forms Cl interstitial defects (Cl_i) besides a small fraction of the Cl is being substituted in the O site. Therefore, we propose that Cl_O and Cl_i defects act as nonradiative recombination paths for the trapped electrons and holes resulting in reduced GE and OE.