Blue Luminescent Center and Ultraviolet-Emission Dependence of ZnO Films Prepared by Pulsed Laser Deposition

Abstract

ZnO thin films were grown on sapphire substrates at a growth temperature of 400 °C by Nd:yttrium–aluminum–garnet (Nd:YAG 1064 nm) pulsed-laser deposition. The effects of oxygen pressure on the structure, stoichiometric composition and optical properties of ZnO thin films were investigated in detail. X-ray diffraction (XRD) shows that the crystal quality is highest for the ZnO film grown at a pressure of 10 mTorr. Optical transmittance, electronic properties and Raman spectra show the increase in the stoichiometric composition ratio of ZnO films with increasing oxygen pressure owing to the reduction in the number of oxygen vacancies (VO) and Zn interstitials (Zni). Photoluminescence (PL) spectra reveal that the UV-emission properties have greater dependence on the stoichiometriy of ZnO films than on the crystal quality. A blue-light emission peak at about 465 nm (E g=2.66 eV) was observed in the PL spectra of ZnO thin films fabricated at various oxygen pressures. This emission peak was ascribed to the electronic transition from the donor energy level of the Zn interstitials to the acceptor energy level of the Zn vacancies (VZn) rather than the oxygen vacancies.

Growth and characterization of ZnO films on (001), (100) and (010) LiGaO2 substrates

“…The E 1 (LO) mode positioned at about 580 cm -1 attributable to the formation of zinc interstitials and oxygen vacancies is not found in this figure, suggesting relatively low defect density in these films [18,19]. For ZnO, the E 2 (high) mode frequency shifts relative to the single crystal value can be used to estimate residual stress in thin films [20,21].…”

Synthesis of a stable sol of ZnO nanoparticles by low-temperature heating of Zn(OH)2 in ethylene glycol containing Zn2+ ions

“…Figures 9(a) 24) It can therefore be inferred that the shift of the Raman peak position of E1(low) involves some contribution of the lattice defects in the obtained ZnO nanoparticles. A steep increase in the Raman band around 1050 cm -1 was also observed with an increase in the concentrations of zinc nitrate hydrate from 0.01 mol/L to 0.1 mol/ L. Windisch, Jr. et al have also reported that the intensity of the Raman bands depends on the change in symmetry caused by defects.…”

Micro-Raman and photoluminescence study of urchin-like ZnO structure assembled with nanorods synthesized by hydrothermal method

“…In this study, it can be estimated that the acceptor level of V zn locates at *0.40 eV above the valence band. The green emission 523 nm (*2.36 eV) are attributed to radiative transitions from the deep donor level of Zn i to acceptor levels caused by singly ionized V zn - [36]. Because the peak positions of the green emission are located at 2.36 eV in this study, the acceptor level of the ionized V zn -locates at *0.61 eV above the valence band.…”