Impact of UV-ozone annealing on the optical and structural properties of ZnO thin films and nanorods

Abstract

ZnO thin films and nanorods are being used for UV optoelectronic applications such as UV-detectors, UVLEDs and Laser diodes because of its large bandgap (3.37 eV) and high excitonic binding energy at room temperature (60 meV). However native point defects in as grown ZnO films need to be suppressed before its device application. Here in this work, a comparative study on the effect of UV-Ozone annealing on the optical properties of ZnO thin films and nanorods have been carried out. Thin films were deposited using RF sputter system and hydrothermal route was used for nanorods growth, followed by UVO annealing for 50 min. Field emission gun scanning electron microscopy (FEG-SEM) confirmed formation of high density nanorods. High resolution X-ray diffraction (HRXRD) results exhibited (002) crystal orientation as the dominant peak for all samples. Calculated grain size for as-grown thin films and nanorods were 27 nm and 37 nm respectively. After UVO annealing it increased to 35 and 47 nm respectively. Room temperature photoluminescence showed enhancement in near band emissions (NBE) for both thin films and nanorods. Maximum enhancement in NBE as compared to as-grown for thin films and nanorods were found to be 6.6 and 3.6 times, respectively. Maximum NBE to DBE integrated area ratio for thin films and nanorods were 0.17 and 0.70 respectively.