Effect of 4He2+ ion irradiation on the optical, electrical, morphological, and structural properties of ZnO thin films

Abstract

Abstract A study of the effect of 2.5 MeV 4He2+ ion irradiation on the optical, electrical, morphological and structural properties of ZnO thin films is presented. Polycrystalline zinc oxide thin films were deposited on soda lime glass substrates using the spray pyrolysis technique. During the process, the substrates’ surfaces were kept at 400, 450 and 500 °C. The samples were analyzed by different techniques and the optical results showed a red shift in the energy band gap after irradiation. It was also confirmed that the wurtzite-type hexagonal structure of the ZnO films remained after irradiation, the crystallite size increased and the lattice parameters decreased due to He2+ irradiation. SEM micrographs revealed that ion irradiation favors the nucleation and the formation of grains in the films. Micrographs showed nanometric particles with spherical and flake-like forms, which depend on the deposition temperature. A decrement in the average particle size of the samples deposited at 400 and 450 °C was observed after irradiation; meanwhile, an increase in the particle size was detected in the film deposited at 500 °C. The resistivity values increased with He2+ ion irradiation.