Photoluminescence spectra of nanocrystalline ZnO films obtained by magnetron deposition technique

Abstract

In this article, the influence of the duration of high-temperature (T = 800 °C) annealing on the transformation of the defective structure and the morphology of thin films from arrays of ZnO nanocrystals synthesized by high-frequency magnetron sputtering was studied using the methods of photoluminescence and atomic force microscopy. On the basis of atomic force microscopy measurements, it was established that ZnO films consist of densely packed grains ranging in size from 40.5 to 49.1 nm. An increase in grain size to statistically significant values over 80 nm is observed as a result of annealing for 60 min. The influence of the high-temperature annealing duration on the transformation of PL spectra of exciton and defects bands and, accordingly, the defect structure of the nanocrystalline ZnO films was determined. In the PL spectra of ZnO nanocrystals, the lines of bound excitons (378 nm, 388 nm) are clearly distinguished in the ultraviolet region. In the visible region, the weak band at 468 nm and fairly intense bands at 559 nm and 683 nm appear, which are characteristic for nanostructured ZnO films obtained by magnetron sputtering. The nature of the specified PL bands is discussed. Differences in the dependence of the intensity of individual PL bands on the duration of annealing are explained by the competition of the recombination mechanisms on non-radiative (Zn_i) and radiative (O_Zn, V_Zn–V_O, V_Zn–2V_O) defect centers.