Structural And Optical Properties Of ZnO Films Deposited By PLD And MOCVD

Zinc Oxide (ZnO) is a wide band-gap semiconductor (3.37 eV at room temperature) with the high exciton binding energy of 60 meV. Since the ultraviolet (UV) lasing from ZnO was realized in 1997, the study on ZnO has attracted a great deal of attention because of the intense commercial interest in developing practical short-wavelength semiconductor diode lasers (SDLs) for the huge market needs.ZnO, which has a wurtzite crystal structure, is a wide band gap, low dielectric constant and high chemical stability semiconductor. Because of its electrical, optical, and piezoelectric properties, epitaxial ZnO thin film has many potential applications, especially in the optoelectronic fields. ZnO-based semiconductor optoelectronic devices include ultraviolet detector, light emitting diodes (LEDs) and laser diodes (LDs), etc.For device application, high quality ZnO films are necessary. ZnO Epitaxial films have been grown by various techniques such as Pulsed Laser Deposition (PLD), Metal-organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), E-beam Evaporation, Sputtering and Atomic Layer Epitaxy (ALE). In this paper, ZnO thin films were deposited on Al₂O₃ (0001), Al₂O₃(1120), MgAl₂O₄ (111) and MgO (100) substrates by PLD and MOCVD. The paper engaged in the research work of influences of different growth conditions on characteristics of ZnO films, especially in the impacts of different substrates and growth temperatures, respectively.The ZnO films were c-axis oriented, but the micro-structure of the ZnO film changed to the one with multi-orientation when the substrate temperature increased to 700℃. It can be observed that the films show a uniform grain size with a columnar structure. There was an abrupt absorption edge at the range of 370-390nm. The photoluminescence spectra of the ZnO films deposited by PLD showed very strong UV emission. The UV emission is due to the recombination of excitons. The photoluminescence spectra of the ZnO films deposited by MOCVD showed verystrong deep-lever emission.The orange luminescence centered at 2 eV is related to the amount of oxygen interstitials (Oi) in the films, and the green band at 2.4 eV is associated with singly ionized oxygen vacancies ( V(] ). The position of thedefect-related band shifts to the blue side of the spectrum as the growth temperature increases.