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M5.3.1

Passivation of Defects in ZnO by Hydrogen Plasma Irradiation Naoki Ohashi, 1 Takamasa Ishigaki, 1 Takashi Sekiguchi,2 Isao Sakaguchi,1 and Hajime Haneda1 Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 Japan 2 Nano-Materials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 Japan

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ABSTRACT Hydrogen doping effects on luminescence properties of bulk ZnO samples were examined by using a pulse-modulated plasma irradiation technique. Three kinds of ZnO samples, including both single- and poly-crystals, were employed as specimens. Secondary-ion-mass-spectroscopy analysis revealed that the surface layer to 100 nm was doped with hydrogen after the irradiation and its concentration was in the order of 1017 cm-3. The efficiency of band edge emission was increased by the hydrogenation. However, the degree of the improvements depended on impurity and defect concentration in the original samples. INTRODUCTION Zinc oxide (ZnO) is a potential compound for optoelectronic applications [1-5]. However, the mechanism for the defect related electron-hole recombination process in ZnO is still unclear, although the control of electronic state of defects is one of the most important issues for the improvement of the performance of ZnO, such as luminescence efficiency and electron mobility. One of the problems attracting researchers' interests is the origin of the green emission. For the defect related problems, most of the attentions were paid to the native defects, such as oxygen vacancy[6] and zinc vacancy[7], and cationic impurities[8]. However, results of the recent investigations into defect chemistry of ZnO indicates that hydrogen impurity in ZnO is of great importance on the properties of ZnO[9-12]. We have reported that irradiation with hydrogen plasma affects on the luminescence properties of ZnO[9-11]. For example, a broad visible (VIS) emission band, found in photoluminescence and cathodoluminescence spectra, were suppressed and ultraviolet (UV) emission intensity was increased after irradiation with hydrogen plasma[9]. This behavior has been understood by passivation of active centers as a result of hydrogen doping. However, the details of this passivation mechanism are unclear. There are several difficulties on the investigation in hydrogen plasma irradiation effects on the properties of ZnO; irradiation damage to the samples and difficulty in qualitative analyses of hydrogen concentration. It is well-known that heating ZnO in reductive ambient, such as heat treatment in hydrogen atmosphere, causes evaporation of ZnO. Moreover, irradiation with plasma causes damage to ZnO surface. Consequently, heat accumulation in ZnO by strong hydrogen plasma irradiation enhances the damaging of ZnO[9]. In the present study, in order to prevent damage to ZnO during hydrogen plasma irradiation and to obtain high flux of hydrogen radical, inductively coupled plasma (ICP) operated in a pulse modulation (PM) mode[13, 14] was used