Deposition of Zinc Oxide Thin Films Using a Surface Reaction on Platinum Nanoparticles
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Deposition of Zinc Oxide Thin Films Using a Surface Reaction on Platinum Nanoparticles Kanji Yasui, Hitoshi Miura and Hiroshi Nishiyama Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan ABSTRACT A new chemical vapor deposition method for the growth of ZnO films using the reaction between dimethylzinc (DMZn) and thermally excited H2O produced by a Pt-catalyzed H2−O2 reaction was investigated. The thermally excited H2O molecules formed by the exothermic reaction of H2 and O2 on the catalyst were ejected from a fine nozzle into the reaction zone and allowed to collide with DMZn ejected from another fine nozzle. The ZnO films were grown directly on a-plane (11-20) sapphire substrates at substrate temperatures of 773-873 K with no buffer layer. X-ray diffraction patterns exhibited intense (0002) and (0004) peaks from the ZnO(0001) index plane. The smallest full width at half maximum (FWHM) value of the ωrocking curve of ZnO(0002) was less than 0.1º. The largest Hall mobility and the smallest residual carrier concentration of the ZnO films were 169 cm2V 1s 1 and 1.7×1017 cm 3, respectively. Photoluminescence (PL) spectra at room temperature exhibited a band edge emission at 3.29 eV, with a FWHM of 104 meV. Green luminescence from deeper levels was generally about 1.5% of the band edge emission intensity. PL spectra at 5 K showed a strong emission peak at 3.3603 eV, attributed to the neutral donor-bound exciton Dox. The FWHM was as low as 1.0 meV. Free exciton emissions also appeared at 3.3757 eV (FXA, n=1) and 3.4221 eV (FXA, n=2). −
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INTRODUCTION Zinc oxide (ZnO) is a useful material for many applications such as surface acoustic wave devices [1], gas sensors [2], photoconductive devices [3], and transparent electrodes [4]. Recently, because of its large bandgap (3.37 eV at RT) and large exciton binding energy (60 meV) [5], its application to optoelectronic devices such as light emitting diodes and laser diodes operating in the ultraviolet region has been intensively investigated [6-12]. Many growth techniques, including molecular beam epitaxy (MBE) [8, 9], pulsed laser deposition (PLD) [7, 10], laser MBE (LMBE) [6], and metal-organic chemical vapor deposition (MOCVD) [11,12], have been used to prepare ZnO thin films. Although MOCVD has many advantages for industrial applications, such as a high growth rate on large surface substrates, a wide selection of metalorganic and oxygen source gases, and purification during the surface reaction, ZnO deposition by conventional MOCVD consumes a lot of electric power to react the source gases and raise the substrate temperature. To overcome this, a more efficient means of reacting oxygen and metalorganic source gases is needed. In addition to the low reaction efficiency, conventional CVD methods yield low-quality ZnO films compared to those prepared by MBE and PLD, due to incomplete reaction between metalorganic and oxygen source gases in the gas phase. If thermally excited water is used to hydrolyze the metalorganic source gases, however,
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