Enhancement in optical properties of ZnO nanorods by UV ozone treatment

Over the past few years, zinc oxide nanorods (ZnO NRs) have started emerging as a promising candidate in the area of optoelectronics and various sensor applications due to their structural advantages over the thin film. Enhancing near band edge emission (NBE) with suppression in the defect state emission (DBE) is a challenging problem for utilizing hydrothermally grown ZnO NRs in device application. In this work, we are reporting improvement in NBE and decrement in the DBE peak intensities with post growth UV-Ozone (UV-O) treatment. Hydrothermal bath process was used to fabricate nanorods on the annealed ZnO seed layer followed by UV-O treatment for 20 minutes. Growth of the nanorods was confirmed using field emission gun scanning electron microscopy (FEGSEM). Room temperature photoluminescence (PL) spectra of sample B shows 1.6 times enhancement of NBE/DBE ratio as compared to as grown sample A. Reduction in the oxygen vacancies was confirmed using high resolution x-ray photoelectron spectroscopy (HRXPS), where it was observed to reduce from 25% for as-deposited sample to 7% for UVO annealed sample, leading to increase of NBE/DBE ratio, as observed from PL spectra. High resolution x-ray diffraction (HRXRD) pattern exhibited dominant (002) peak from both samples. A slight right shift was observed in HRXRD peak which suggest improvement in stoichiometric ratio for UV-O treated sample.