Visible Light Emission from ZnO Nanorods Array under Lateral Electric Field Application
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Visible Light Emission from ZnO Nanorods Array under Lateral Electric Field Application Takashi Hirate, Keita Yamazaki and Tomomasa Satoh Department of Electrical, Electronic and Information Technology Faculty of Engineering, Kanagawa University 3-27 Rokkakubashi, Kanagawa-ku, Yokohama, 221-8686, Japan ABSTRACT We study on electrical and light emitting characteristics of ZnO nanorods array when an electric field is applied in lateral direction to the axis of ZnO nanorods. ZnO nanorods grown on an insulator substrate are isolated with each other, i.e. there is no continuous nucleation layer of ZnO at the base of nanorods. When the applied lateral electric field is weak, no electric current and no light emission are observed. When the electric field becomes strong, however, an electric current begins to flow and bluish white light is emitted in the form of many streaks. These light streaks start from cathode and travel in all directions.
INTRODUCTION Zinc oxide (ZnO), a wide-direct-bandgap (3.37 eV) semiconductor, is an attractive II-VI compound semiconductor material for various optoelectronic devices. The growth of various nanostructures of ZnO and application of these nanostructures have been reported [1-7], and ZnO has been considered as a promising material for nanodevices. We have studied an application of ZnO nanorods to field emission devices. In this paper we report on fabrication of ZnO nanorods isolated with each other on an insulating substrate by chemical vapor deposition (CVD) and on electrical and light emission characteristics of these nanorods when electric field is applied in the lateral direction of nanorods. EXPERIMENT We use glass substrates coated with electron-beam-deposited SiO2 of 50 nm thickness. Carbon layer of 150 nm thickness is deposited on the selected regions of SiO2 layer and these regions are used as cathode and anode electrodes. Figure 1 shows a pattern diagram of a substrate. The growth method is CVD method cooperated with laser ablation that is developed by us. The growth equipment is similar that reported before [1, 3]. This is basically a low-pressure thermal CVD system. The precursors are metal Zn vapor and O2. Zn vapor is introduced into a deposition chamber through a fine orifice. N2 is used as carrier gas to transport Zn vapor from Zn
vaporization chamber to deposition chamber. O2 is also introduced into deposition chamber. An Au (99.999%) target (10 mm diameter, 10 mm height) is set in deposition chamber. A pulsed Nd:YAG laser beam (wavelength =1.064 μm, pulse width = 10 ns, repetition frequency = 10 Hz) irradiates the Au target surface through the quartz window. Following to this laser ablation the growth of ZnO nanorods is initiated. The growth temperature is 515 C and pressure is 13 Pa. After the growth of ZnO nanorods, ZnO nanorods grown on peripheral strip area of about 1 mm width are removed to confirm electrical insulation between Cathode Anode nanorods area and the other parts as 1.5[mm] 30° ZnO nanorods shown in Figure 1. Lead wires are bonded to each electrode u
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