Catalyst-free Growth of Large Scale Ga 2 O 3 Nanowires
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Catalyst-free Growth of Large Scale Ga2O3 Nanowires
Ko-wei Chang, Sai-chang Liu, Liang-Yih Chen, Franklin Chau-Nan Hong, and Jih-Jen Wu Department of Chemical Engineering, National Cheng Kung University Tainan, Taiwan ABSTRACT Large scale of straight Ga2O3 nanowires is grown on a fused silica substrate by a simple catalyst-free CVD method using Ga metal and N2 / H2O reactants. The Ga2O3 nanowires with diameters ranging from 60 to 150 nm can be as long as several micrometers. XRD and TEM analyses indicate that the Ga2O3 nanowires exhibit a monoclinic structure. PL characteristic of the Ga2O3 nanowires shows a UV emission of 375 nm at room temperature.
INTRODUCTION The synthesis of nanometer scale one-dimensional materials, for example β-SiC [1-3], GaN [4,5], In2O3 [6], and Si [7,8], has received intensive research because of their great potential for fundamental studies of the roles of dimensionality and size in their physical properties as well as for the application to optoelectronic nanodevices [9]. Gallium oxide, β-Ga2O3, is a wide band gap compound ( Eg = 4.9 eV), and has potential applications in optoelectronic devices including flat panel displays, solar energy conversion devices, and high temperature stable gas sensors [10,11]. Even more, upon optical excitation through the band gap, β-Ga2O3 exhibit up to three different emissions, UV, blue, and green [12-14]. Recently, β-Ga2O3 nanowires have been synthesized by an arc discharge method [15] , and physical deposition [16]. Here, we present a simple catalyst-free CVD approach for the growth of the straight β-Ga2O3 nanowires at a temperature of 800oC.
EXPERIMENTAL DETAILS The schematic representation of the β-Ga2O3 nanowires growth apparatus is shown in Fig. 1. Typically, an excess amount of molten gallium (Alfa Aesar, 99.99%) was placed on the fused silica substrate A (1x1cm2) that was put in the end of the Al2O3 boat. The fused silica substrate B (1x1cm2) was put away from substrate A about 3mm. An Al2O3 plate (4x4cm2) put on the
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Fig. 1 Schematic diagram of the high temperature furnace used for the synthesis of the straight β-Ga2O3 nanowires. top of the Al2O3 boat was used to increase the reactants space time in the Al2O3 boat. Then the Al2O3 boat was inserted into the center of a 3 in. diameter furnace. Before the synthesis process, the furnace was evacuated to a base pressure of 1x10-2 Torr. The temperature of the furnace was increased to 800oC within 1 hr at a constant N2 flow of 200 sccm and a pressure of 500 Torr. As the temperature reached 800oC, the H2O vapor was carried from an isothermal bath by another N2 flow into the furnace. The synthesis processes were conducted under the following condition: furnace temperature, H2O vapor rate, N2 flow rate, furnace pressure of 800oC, 3 sccm, 200 sccm and 500 Torr, respectively. After the 6-hr reaction, the furnace was cooled to room temperature and white products were deposited on the fused silica substrate B. The morphology and size distribution of the products were exami
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