Annealing Effects of ZnO Nanorods on DC Inorganic Electroluminescent Device Characteristics
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Annealing Effects of ZnO Nanorods on DC Inorganic Electroluminescent Device Characteristics Shinya Sasaki, Hiroshi Miyashita, Takashi Kimpara, Tomomasa Satoh and Takashi Hirate Department of Electrical, Electronics and Information Engineering Faculty of Engineering, Kanagawa University 3-27 Rokkakubashi, Kanagawa-ku, Yokohama, 221-8686, Japan ABSTRACT We fabricated a DC inorganic electroluminescent (EL) device whose structure is ITO electrode / ZnS:Mn / ZnO (Mn) nanorods / p-/p++-Si(111) / Au electrode. ZnO nanorods were grown by chemical vapor deposition method combined with laser ablation. ZnS:Mn and ITO were deposited by electron-beam-deposition. We studied on annealing effects of ZnO nanorods on the electrical and electroluminescent characteristics of this device. The device without annealing showed a low breakdown voltage, and any EL emission could not be observed. On the other hand, the device with annealing showed higher impedance and higher breakdown voltage, and the EL emission from the ZnS:Mn layer was observed. An intense EL emission was observed from a peripheral of ITO electrode. An EL emission from the inside area of ITO electrode was very weak. INTRODUCTION Inorganic thin film electroluminescent devices, which have been practically used, have a double insulator structure of electrode / insulator layer / active layer / insulator layer / electrode and can only be operated with an AC high driving voltage due to the insulator layers [1, 2]. This is a reason why the devices are not widely used at present. We reported on the fabrication of ZnO nanorods by chemical vapor deposition combined with laser ablation of Er [3], and proposed an electroluminescent device including ZnO nanorods layer and pointed out that this device whose structure was an ITO electrode / ZnS:Mn / ZnO (Er) nanorods / p-/p++-Si(111) / Au electrode could be operated with a DC driving voltage [4]. The devices without ZnO nanorods or with ZnO film did not show an EL emission. We studied on fabrication of ZnO nanorods layer by laser ablation of Mn and obtained the ZnO nanorods layer with higher number density that is considered to be suitable for EL devices. In this paper we report on the fabrication of an ITO electrode / ZnS:Mn / ZnO (Mn) nanorods / p-/p++-Si(111) / Au electrode device and on annealing effects of ZnO (Mn) nanorods on the electrical and electroluminescent characteristics of this device.
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EXPERIMENTAL DETAILS Table 1. Growth conditions for ZnO nanorods.
Figure 1. Growth equipment for ZnO nanorods.
Zn Evaporation Temperature [℃] Growth Temperature [℃] Flow Rate of N2 for Zn [SCCM] Flow Rate of N2 for O2 [SCCM] Flow Rate of O2 [SCCM] Growth Pressure [Pa] Growth Time [min] 2 Laser Irradiaded Area [mm ] Laser Energy Density [J/Shot・mm2] Laser Pulse Frequency [Hz]
580 600 5.0 1.5 1.5 40 15 0.13 0.92 10
ZnO nanorods were grown on a p-/p++-Si (111) substrate by chemical vapor deposition method combined with laser ablation that was developed by us [3, 4]. The growth equipment is schematically shown in figure 1
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