Hyo-Kyung Cho

The effect of diameter change on photoelectrochemical water splitting was investigatedin depth for ZnO nanorods. ZnO nanorods were grown on SiO2/Si and indium tin-oxidesubstrates by the hydrothermal growth method. By controlling the concentration ratiobetween zinc nitrate hexahydrate (ZNT) and hexamethylenetetramine (HMTA)nanorod diameters were changed from 45 to 275 nm, in which the diameter decreasedwith decreasing the ratio. Photoelectrochemical properties of ZnO nanorods withdiameters from 4

Both perovskites LaNiO3 and LaCuO3 have a limitation associated with phase transitions for high-temperature thermoelectric applications. The optimized conditions were investigated to obtain the LaNi1-xCuxO3-δ perovskite single phase showing a Cu-doping effect into Ni sites against unintended deoxidized phases. Three advantages of synergetic effects due to the simultaneous presence of nickel and copper were investigated: a low melting temperature of CuO as compared to that of NiO, the absence of

Al2O3 dielectric layers with a dense and atomically flat surface were grown at relatively low temperatures of 150 °C by atomic layer deposition (ALD) for use as the gate oxide of transparent and flexible oxide thin-film-transistors (TFTs). The ALD growth of the high quality Al2O3 with a less rough surface at 120 °C allowed us to use the liftoff process without wet chemical etching and made the fabrication method for flexible electronics simple. This also improved the electrical performance of th

We report on n-ZnO/p-GaN heterojunction light-emitting diodes (LEDs) fabricated from ZnO films, for which the electrical properties and oxygen contents were controlled by post-annealing. Intense violet emission with a peak wavelength near 381 nm was observed in the electroluminescence (EL) spectra and was attributed to the near-band-edge emission of the n-ZnO layer. With increasing annealing time, however, the EL peak position broadened and showed a strong deep-level emission. The LEDs were yell

We have deposited ZnO thin films on Si(111) substrates with and without a low temperature-grown ZnO buffer layer by using radio-frequency (rf) magnetron sputtering. The microstructural properties of ZnO/Si heterostructures have been investigated by using X-ray diffraction (XRD), pole-figures and transmission electron microscopy (TEM) measurements. The results of XRD, pole figures and TEM showed that both ZnO thin films with and without an embedded buffer layer had highly c-axis preferred orienta

The one-dimensional ZnO nanostructures prepared through thermal evaporation under various cooling down procedures by changing the flow rates of the carrier gas and the reactive gas were investigated. The nanorod structures were changed into the nanonail types with a broad head through the reduction of the flow rate of the carrier gas. The decrease of the reactive gas reduced the length of the nail heads due to the limited mass transport of reactive gas. The intensity ratio of the ultraviolet emi

Structural and optical properties of InGaN/GaN multiple triangular quantum well (QW) structures with different threading dislocation (TD) densities of 1.5×108 (sample A) and 4.5×108 cm-2 (sample B) have been studied. High resolution transmission electron microscopy and x-ray diffraction analysis showed more fluctuation of local In composition in the sample B, which was attributed to the stress field created by the dislocations as it provides a driving force for the migration of In atoms towards

The wide band-gap semiconductor NiO has p-type characteristics and is an alternative to p-ZnO, due to conduction mechanisms coming from the Ni vacancies and O interstitials. The correlation between the electrical properties and point defects was studied with NiO thin films grown by sputtering at various temperatures and in pure Ar and O2 atmospheres. The p-type characteristics of the NiO thin films were double-checked by Hall-effect and Seebeck coefficient measurements. Below 300 °C, the electri

We deposited Ni (13 nm) / Au (30 nm) layers on p-GaN by using the dc sputtering method in order to produce low-resistivity Ohmic contacts. The Ni (13 nm) / Au (30 nm) contact layers were annealed in air for 15 min at various temperatures. The electrical and the structural properties of the Ni/Au contact to p-GaN were investigated. The current-voltage measurement showed that the resistance of the as-deposited sample was very high. However, the sample annealed at 600 ℃ showed Ohmic-like behavior w

Transparent multilayer indium-zinc-oxide (IZO) films are designed and fabricated to achieve lowresistance and highly-transparent electrodes on glass substrates. IZO multilayers were fabricated by inserting an In2O3 - 90wt% ZnO (Zn-rich IZO) thin film between two layers of In2O3-10 wt% ZnO (In-rich IZO) thin films. The In-rich IZO/Zn-rich IZO/In-rich IZO multilayer film exhibited a low resistance of 4.6 × 10−5 Ω·cm and a high transparency of about 80 %. In comparison with IZO films without a Zn-r

by changing the reactor pressure in the chemical vapor transport method. The photoelectrochemical(PEC) properties of ZnO nanostructures were investigated by using an ultraviolet lampwith a wavelength of 365 nm and a measured intensity of 0.4 mW/cm2. Photocurrent densities of0.61, 0.47, and 0.37 mA/cm2 were obtained for nanowires, nanosheets, and nanorods, respectively. The photoconversion efficiencies of these ZnO nanostructures under ultraviolet illumination werecalculated as 73.1, 57.3, and 41

The excitonic carrier dynamics taking place in In$_x$Ga$_{1-x}$N/GaN multi-quantum-well systems have been studied by using low temperature picosecond-time-resolved photoluminescence (LT-TRPL), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Dynamic time of flight secondary ion mass spectrometry (TOF-SIMS), and quantum mechanical simulation methods. Both time-integrated and time-resolved photoluminescence spectra of In$_x$Ga$_{1-x}$N/GaN multi-qu

유기금속 화학기상 증착 (metal-organitic chemical vapor depositin)방법을 이용하여 사파이어 기판 위에 저 결함 GaN의 이종접합 수평성장을시행하고 그 위에 근 자외선 발광 다이오드 (light-emitting diode: LED)에피 층 (epitaxial layers)을 성장하였다. 사파이어 기판 표면은 SiO$_2$ 줄무늬 마스크가 형성되었으며 그 두께는 200 - 500 \AA 이었다. 먼저 줄무늬 마스크가 형성된 기판 표면에 핵 형성 층을 성장한 후, 그 위에 고온 GaN 수평성장이 진행되었다. 고온 수평 성장된 저 결함 GaN 박막에서 나선형과 혼합형 관통전위 (threading dis-location)의 밀도는 전 영역에 걸쳐 약 2.5 $\times$ 10$^7$ cm$^{-2}$ 이었으며 결정학적 기울어짐 현상은 평탄한 사파이어 기판 위에 성장된 GaN 박막 수준으로 낮아졌다. 저 결함 GaN 박막 위에 성정된 근 자외선 LED 에피 층

The effects of gas atmosphere and in-situ thermal annealing in buffer layers on the characteristic of the ZnO grown by RF magnetron sputtering have been investigated. It was shown that the introduction of buffer layers grown at the gas atmospheres of the mixed Ar/O2 and the in-situ thermal treatment of the ZnO buffer layer improved the structural and optical properties. In addition, the ZnO films on the buffer layer thermal-annealed at N2 gas ambience showed the strong emission of the near band

Ultraviolet (UV), 365-nm light-emitting diodes (LEDs) were grown on an AlGaN template on patterned sapphire substrates (PSS) and then compared with those grown on a conventional GaN template. Complete coalescence was achieved by using AlGaN up to 4.9% Al composition, although the AlGaN template displayed more dislocations than the GaN template. The 365-nm UV LEDs on the AlGaN template showed no emission absorption in the template, as seen in the GaN template, because AlGaN is sufficiently far fr