Characteristic of hydrogenated Ga-doped ZnO films grown by DC magnetron sputtering using H 2 /Ar gas
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Characteristic of hydrogenated Ga-doped ZnO films grown by DC magnetron sputtering using H2/Ar gas Satoshi Takeda and Makoto Fukawa Research Center, Asahi Glass Co., Ltd. 1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755, Japan ABSTRACT We report characteristics of sputtered Ga-doped ZnO films grown in pure Ar (Ar-films) and H2/Ar gas mixture (H2/Ar-films). With increasing water partial pressure (PH2O), the resistivity of Ar-films significantly increased due to the decrease in both free carrier density and Hall mobility. The transmittance in the wavelength region of 300-400 nm for the films also increased with increasing PH2O. However, no significant PH2O dependence of the electrical and optical properties was observed for H2/Ar-films. Secondary ion mass spectrometry analysis revealed that hydrogen concentration in the Ar-films increased with increasing PH2O, indicating that the origin of the incorporated hydrogen is attributed to the residual water vapor in the coating chamber. On the contrary, the hydrogen concentration in H2/Ar-films was almost constant irrespective of PH2O and the concentration is obviously higher than that of Ar-films, indicating that the hydrogen primarily comes from H2 gas and the adsorption species due to H2 gas preferentially adsorb to the growing film surface over residual water vapor. Consequently, the effect of PH2O on the crystal growth was significantly reduced by H2 gas introduction, resulting in stability improvement. INTRODUCTION Hydrogen is the smallest and lightest element, so that it easily diffuses into materials. The diffused hydrogen can have effects on the material properties [1,2]. Therefore, it is important to clarify the role of hydrogen to control the material properties. Secondary ion mass spectrometry (SIMS) is widely used to detect hydrogen because of its excellent sensitivity and high depth resolution. Also, an isotope analysis is possible in this method, so that SIMS analysis using deuterium (D2) is considered to be useful to elucidate the origin of hydrogen. In the present study, we applied the SIMS analysis to investigate the hydrogen in Ga-doped ZnO (GZO) films grown by DC magnetron sputtering. GZO is a typical transparent and conductive oxide, which is degenerate wide band-gap semiconductors with low resistance and high transparency in the visible wavelength range, and is one of the promising materials in optoelectronic devices such as transparent electrodes in flat panel displays and solar cells [3,4]. Here, GZO films were deposited under pure Ar and H2/Ar mixture gas. The effects of H2 gas introduction on the stability of both electrical and optical properties of the films versus residual water pressures (PH2O) were investigated in detail.
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EXPERIMENTAL DETAILS The GZO films were deposited onto glass (Corning 7059) with a thickness of 150-180nm by DC magnetron sputtering at room temperature under various residual water pressures (PH2O). Quadrupole mass spectrometry analysis revealed that base pressure was primarily due to PH2O. Thus, PH2O were co
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