Nak-Won Jang

Post-annealing in oxygen ambient for (Ba, Sr)TiO3 thin films prepared by pulsed laser deposition

Abstract Structural and electrical properties of (Ba0.6Sr0.4)TiO3 thin films prepared by pulsed laser deposition were investigated to verify influences of post-annealing in oxygen ambient. Increase of post-annealing time in oxygen ambient resulted in not only grain growth but also improvement of crystallinity in BST films. Although the post-annealing in oxygen ambient resulted in the increase of surface roughness, it assisted the dielectric constant increase by eliminating oxygen vacancies. The electrical property enhancement including high dielectric constant and low leakage current density was associated with introducing high pressure of oxygen during the post-annealing.

Structural and electrical properties of PLZT films on ITO-coated glass prepared by a sol-gel process

Abstract PLZT films prepared by a sol-gel process were fabricated on indium tin oxide (ITO)-coated glass substrates using rapid thermal annealing (RTA). The films crystallized into the perovskite phase when annealed at 750°C for 5 min. X-ray diffraction (XRD) and Raman spectroscopy results indicate that the morphotropic phase boundary of PLZT films shifts toward the Ti-rich side, in contrast to that of bulk ceramics. A dielectric constant of 1270 for the 2/55/45 composition was the maximum value observed. With increasing Zr content in the 2 mol% La modified films, the coercive field decreased from 52.9 to 30 kV/cm and the remanent polarization increased from 22.7 to 50.6 μC/cm 2 . Optical transmittance increased by increasing optical isotropy as the Zr content increased.

The Effect of Buffer Layer on ZnO Nanorods on PES Substrate.

In general, growing ZnO nanorods with the hydrothermal method requires the deposition of ZnO buffer layers. This is the most essential step, because the morphology of ZnO nanorods is strongly influenced by the buffer layer on a flexible substrate. In this work, we study the effect of the buffer layer when ZnO nanorods are grown. ZnO nanorods were grown on ZnO-buffered PES substrates with the hydrothermal method. As a result, it was found that the ZnO buffer layer using PLD had excellent characteristics compared with the ZnO buffer layer using sputtering.

A Study on the Thermal and Optical Properties of a LED Chamber Light for Vessels

AD Revised October 24, 2014; Accepted November 26, 2014)Abstract: Recently, LED is widely used in the kinds of display devices or lighting. In this paper, we fabricated LED chamber light for naval vessels to replace to conventional chamber light using incandescent lamp. The LED package of chamber light was designed with luminous intensity of 5.5 cd, color temperature of 6,000 ± 500 K, forward voltage of 3〜3.2 V and input current of 60 mA. A LED module was composed of 36 LED packages and metal PCB. The VF and luminous intensity of LED package were getting down when temperature increased. The temperature of LED chamber light was measured by changing the number of LED package and applied current for one hour when an electric current flow. The heat transfer capability have been improved by using metal PCB. The power consumption of LED chamber light reduced by 86% compared to the conventional chamber light using incandescent lamp.Keywords: LED, Chamber light, Vessel, Power consumption, Forward voltage, Luminous intensity

The Structural Characteristics of Mg x Zn 1-x O Thin Films with Sputtering Power by Co-sputtering Method

The effect of co-sputtering condition on the structural properties of thin films grown by RF magnetron co-sputtering system was investigated for manufacturing UV LED. 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 thin films have sufficient crystallinity on the high ZnO power. The EDS analyzed showed that the Mg content in the films decreased from 3.99 to 24.27 at.% as the RF power of ZnO target increased. The Mg content in the films could be controlled by co-sputtering power.

The Characteristics of Mg 0.1 Zn 0.9 O Thin Films on PES Substrate According to Fabricated Conditions by PLD

Concern for the TOS (Transparent Oxide Semiconductor) is increasing with the recent increase in interest for flexible device. Especially MgZnO has attracted a lot of attention. , which ZnO-based wideband-gap alloys is tuneable the band-gap ranges from 3.36 eV to 7.8 eV. In particular, the flexible substrate, the crystal structure of the amorphous as well as the surface morphology is not good. So research of MgZnO thin films growth on flexible substrate is essential. Therefore, in this study, we studied on the effects of the oxygen partial pressure on the structural and crystalline of thin films. MgZnO thin films were deposited on PES substrate by using pulsed laser deposition. We used XRD and AFM in order to observe the structural characteristics of MgZnO thin films. UV-visible spectrophotometer was used to get the band gap and transmittance. Crystallization was done at a low oxygen partial pressure. The crystallinity of MgZnO thin films with increasing temperature was improved, Grain size and RMS of the films were increased. MgZnO thin films showed high transmittance over 80% in the visible region.

The Characteristics of Multi-layer Structure LED with Mg x Zn 1-x O Thin Films

The effect of co-sputtering condition on the structural properties of thin films grown by RF magnetron co-sputtering system was investigated for manufacturing ZnO/MgZnO structure LED. 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 film decreased. LED was manufactured using ZnO/MgZnO multi-layer on p-GaN/ substrate. Threshold voltage of multi-layer LED was appeared at 8 V, and it was luminesced at wave length of 550 nm.

Effect of Oxygen Pressure on the Structure Properties of Mg 0.5 Zn 0.5 O Thin Films Grown by Pulsed Laser Deposition

In this work, we study on the effects of the oxygen pressure on the structural and crystalline of MgZnO thin films. MgZnO thin films were deposited on p-Si (111) substrates by using pulsed laser deposition. The X-ray diffraction analysis and energy-dispersive X-ray results revealed that as the oxygen pressure increased and Mg content in the MgZnO films decreased. Also Crystal structure was changed from cubic rock salt to hexagonal wurtzite. Alpha step and atomic force microscopy results showed that the thickness of the films are about 100 nm, and it has been found that the MgZnO (002) preferred orientation were deposited with increasing the oxygen pressure. Therefore, the effect of the preferred orientation, the crystallization grew in the form of the columnar; Grain size and RMS of the films were increased with increasing oxygen pressure.

Effect of Ambient Gases on Thermal Annealed ZnO films deposited on Si(111) Substrates

Zinc oxide films were deposited on Si (111) substrates by radio-frequency (rf)sputtering at a room temperature and post annealed in Na, air, and ambient at temperatures between for 2 hrs. The properties were investigated by atomic force microscope (AFM), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and photoluminescence (PL). Our experiments demonstrated that ZnO films have the better crystal quality for post thermal annealing and especially in ambient. Even though thermal annealing reduced deep level emission somewhat, for further getting rid off deep level emission, oxygen contents should be adjusted. In our results, ambient gave the best structural and optical properties.

Effect of Oxygen Contents in Thermal Annealed ZnO films on Structural and Optical Properties

We studied that structural and optical properties of ZnO films depend on oxygen contents. ZnO films were deposited on Si (111) substrates at room temperature by rf sputtering system and the thickness of films was 100 nm. The ZnO films were annealed in thermal furnace for 2 h at 800 and in , and air ambient gases to control oxygen contents. We used AES, PL, XRD, AFM. As our result, crystal quality and luminescence improved until O/Zn is 1. However, when O/Zn ratio Is larger than 1, the structural and optical properties were getting worse.