• Korean Journal of Materials Research
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• v.20 no.5
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• pp.235-240
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• 2010

We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of $500^{\circ}C$. It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at $250^{\circ}C$ and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

• Applied Science and Convergence Technology
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• v.26 no.2
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• pp.30-33
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• 2017

ZnO thin films which were deposited by RF magnetron sputtering system were annealed by furnace and insitu heat treatment methods. We investigated the effect of heat treatment method on physical properties of ZnO thin films. The structural and optical properties of ZnO thin films were improved by heat treatment. Through the annealing treatment of ZnO film by furnace, the good crystallinity and ultraviolet emission were obtained. These results are attributed to the improved formation of Zn-O bond in ZnO thin film annealed at by furnace. We confirm that the formation of Zn-O bond plays an important role in obtaining the excellent structural and optical properties of ZnO thin films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.811-816
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• 2012

The effect of co-sputtering condition on the structural properties of $Mg_xZn_{1-x}O$ thin films grown by RF magnetron co-sputtering system was investigated for manufacturing ZnO/MgZnO structure LED. $Mg_xZn_{1-x}O$ thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The ZnO thin films have sufficient crystallinity on the high RF power. As RF power of ZnO target increased, the contents of MgO in the $Mg_xZn_{1-x}O$ film decreased. LED was manufactured using ZnO/MgZnO multi-layer on p-GaN/$Al_2O_3$ substrate. Threshold voltage of multi-layer LED was appeared at 8 V, and it was luminesced at wave length of 550 nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.164-169
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• 2013

The effect of co-sputtering condition on the structural properties of $Mg_xZn_{1-x}O$ thin films grown by RF magnetron co-sputtering system was investigated for manufacturing UV LED. $Mg_xZn_{1-x}O$ thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The $Mg_xZn_{1-x}O$ thin films have sufficient crystallinity on the high ZnO power. The EDS analyzed showed that the Mg content in the $Mg_xZn_{1-x}O$ films decreased from 3.99 to 24.27 at.% as the RF power of ZnO target increased. The Mg content in the $Mg_xZn_{1-x}O$ films could be controlled by co-sputtering power.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.310-310
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• 2012

ZnO thin films were grown on porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The optical properties of the ZnO thin films grown on PS were studied using room-temperature, low-temperature, and temperature-dependent photoluminescence (PL). The full width at half maximum (FWHM) of the near-band-edge emission (NBE) from the ZnO thin films was 98 meV, which was much smaller than that of ZnO thin films grown on a Si substrate. This value was even smaller than that of ZnO thin films grown on a sapphire substrate. The Huang-Rhys factor S associated with the free exciton (FX) emission from the ZnO thin films was found to be 0.124. The Eg(0) value obtained from the fitting was 3.37 eV, with ${\alpha}=3.3{\times}10^{-2}eV/K$ and ${\beta}=8.6{\times}10^3K$. The low- and high-temperature activation energies were 9 and 28 meV, respectively. The exciton radiative lifetime of the ZnO thin films showed a non-linear behavior, which was established using a quadratic equation.

• Journal of the Korean Vacuum Society
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• v.22 no.1
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• pp.20-25
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• 2013

ZnO:Al thin films deposited by RF magnetron sputtering were post-annealed and the electrical and optical properties of ZnO:Al thin films were investigated before and after anneling. We confirmed that the ZnO:Al thin film was affected by post-annealing temperature. As post-annealing temperature increases, crystallinity and transmittance in visible area (400~800 nm) of ZnO:Al thin films decreased. While sheet resistance of thin films increased sharply with increasing to $400^{\circ}C$. This result is due to reduce of carrier concentration caused by absorption of $O_2$ or $N_2$ at surface of thin film.

• Transactions on Electrical and Electronic Materials
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• v.13 no.6
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• pp.305-309
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• 2012

In this study, ZnO nanorods and $SnO_2$-CuO heterogeneous oxide were grown on membrane-type gas sensor platforms and the sensing characteristics for carbon monoxide (CO) were studied. Diaphragm-type gas sensor platforms with built-in Pt micro-heaters were made using a conventional bulk micromachining method. ZnO nanorods were grown from ZnO seed layers using the hydrothermal method, and the average diameter and length of the nanorods were adjusted by changing the concentration of the precursor. Thereafter, $SnO_2$-CuO heterogeneous oxide thin films were grown from evaporated Sn and Cu thin films. The average diameters of the ZnO nanorods obtained by changing the concentration of the precursor were between 30 and 200 nm and the ZnO nanorods showed a sensitivity value of 21% at a working temperature of $350^{\circ}C$ and a carbon monoxide concentration of 100 ppm. The $SnO_2$-CuO heterogeneous oxide thin films showed a sensitivity value of 18% at a working temperature of $200^{\circ}C$ and a carbon monoxide concentration of 100 ppm.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.475-482
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• 2005

Zn$_{l-x}$Co$_{x}$O (x = 0.05 - 0.20) films were grown on Coming 7059 glass by sol-gel process. A homogeneous and stable Zn$_{l-x}$Co$_{x}$O sol was prepared by dissolving zinc acetate dihydrate (Zn(CH$_{3}$COO)$_{2}$$\cdot$2H$_{2}$O), cobalt acetate tetrahydrate ((CH$_{3}$)$_{2}$$\cdot$CHOH) and aluminium chloride hexahydrate (AlCl$_{3}$ $\cdot$ 6H$_{2}$O) as solute in solution of isopropanol ((CH$_{3}$)$_{2}$$\cdot$CHOH) and monoethanolamine (MEA:H$_{2}$NCH$_{2}$CH$_{2}$OH). The films grown by spin coating method were postheated in air at 650°C for 1 h and annealed in the condition of vacuum (5 $\times$ 10$^{-6}$ Torr) at 300$^{\circ}C$ for 30 min and investigated the nature of c-axis preferred orientation and physical properties with different Co concentrations. Znl_xCOxO thin films with different Co concentrations were well oriented along the c-axis, but especially a highly c-axis oriented Zn$_{l-x}$Co$_{x}$O thin film was grown at 10 at$\%$ Co concentration. The transmittance spectra showed that Zn$_{l-x}$Co$_{x}$O thin films occur typical d-d transitions and sp-d exchange interaction became activated with increasing Co concentration. The electrical resistivity of the films at 10 at$\%$ Co had the lowest value due to the highest c-axis orientation. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetic properties appeared, respectively. The characteristics of the electrical resistivity and room temperature ferromagnetism of Zn$_{l-x}$Co$_{x}$O thin films suggested the possibility for the application to dilute magnetic semiconductors.

• Journal of the Korean Magnetics Society
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• v.11 no.4
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• pp.168-172
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• 2001

Co-Zn ferrite thin films grown on thermally oxidized silicon wafers were fabricated by a sol-gel method. Magnetic and structural properties of Co-Zn thin films were investigated by using x-ray diffractometer (XRD), atomic force microscopy (AFM), auger electron spectroscopy (AES) and a vibrating sample magnetometer (VSM). Co-Zn ferrite thin films annealed at 400 $^{\circ}C$ presented have only a single phase spinel structure without any preferred crystallite orientation. Their surface roughness of Co-Zn ferrite thin films was shown as less than 3 nm and the grain size was about 40 nm for annealing temperatures over 600 $^{\circ}C$. A moderate saturation magnetization of Co-Zn ferrite thin films for recording media was obtained in this study and there is no significant difference of their magnetic property with those external fields of parallel and perpendicular to planes of the films. The maximum value of the coercivity was obtained as 1,900 Oe for Co-Zn ferrite thin film annealed at 600 $^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.372-375
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• 2017

ZnO thin films were deposited by RF magnetron sputtering and then diffused by using an As source in the ampouletube. Also, the ZnO p-n homojunction was made by using As-doped ZnO thin films, and its properties were analyzed. After the As doping, the surface roughness increased, the crystal quality deteriorated, and the full width at half maximum was increased. The As-doped ZnO thin films showed typical p-type properties, and their resistivity was as low as $2.19{\times}10^{-3}{\Omega}cm$, probably because of the in-diffusion from an external As source and out-diffusion from the GaAs substrate. Also, the ZnO p-n junction displayed the typical rectification properties of a p-n junction. Therefore, the As diffusion method is effective for obtaining ZnO films with p-type properties.