Comparative study of the effect of H 2 addition on ZnO films grown by different zinc and oxygen precursors
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In this study, the authors have comparatively studied the influence of H2 addition on the structures and properties of ZnO films grown by metal organic (MO) chemical vapor deposition with dimethyl zinc and diethyl zinc as zinc precursors and N2O and O2 as oxygen sources, respectively. Various characterization methods, like x-ray diffraction, Raman scattering, Hall effect, photoluminescence, and atomic force microscopy, have been utilized, showing that H2 has different effects on different MO precursors and oxidants. The H2 addition has significantly improved the crystal structural quality of ZnO thin films for the case of dimethyl zinc source, but an opposite effect has been found for the case of diethyl zinc. Moreover, the H2 addition can significantly improve the optical properties of the ZnO films, regardless of the zinc MO sources used, with the surface morphology improved too. The suppression of carbon-related contaminations depends on the use of different precursors and whether H2 is added. By analyzing the experimental results, we have given the effects of H2 on the decomposition of the discussed MO precursors and oxidants, the proposed mechanism could be used in understanding the experimental data.
I. INTRODUCTION
ZnO is a wide band gap semiconductor material with a direct band gap of 3.37 eV at room temperature and a free exciton binding energy of 60 meV, which makes ZnO material hopefully suitable for the fabrication of light emitting diodes or even laser diodes at short wave length. Since 1996, when scientists in Japan and Hong Kong achieved the UV lasing of ZnO films at room temperature for the first time, the research on the ZnO material has become a hot topic in the field of photonics.1,2 Molecular beam epitaxy, pulsed laser deposition, and metal organic chemical vapor deposition (MOCVD) have been used to prepare high-quality ZnO films. Among them, the MOCVD technique has received much attention due to its possibility to achieve multi-piece uniform film growth in a large scale with an excellent crystalline quality, a smooth surface, and an abrupt heterointerface. In the MOCVD growth of ZnO, different zinc metal organic (MO) precursors and oxygen sources have been used and studied by many research groups. Dimethyl zinc (DMZn) and diethyl zinc (DEZn) are the mostly used zinc precursors. Our previous work showed that ZnO thin films grown by the DMZn precursor have a high content Contributing Editor: Joan M. Redwing Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2015.81 J. Mater. Res., Vol. 30, No. 7, Apr 14, 2015
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of carbon impurities, while the samples grown by the DEZn precursor have superior structural and optical properties with a low concentration of carbon impurities. Also, the kind of zinc MO precursors has shown a significant influence on the surface morphology of ZnO thin films.3 In the study of Oleynik and Adam, they have made a comparison among different oxygen sources in the ZnO MOC
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