• 한국전기전자재료학회논문지
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• 제23권3호
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• pp.222-227
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• 2010

ZnO nanorods array have been grown on the seed crystal coated Si(100) substrate by hydrothermal method. The growth, structural and optical properties of ZnO nanorods array were investigated with a variation of precursor concentration from 0.01 M to 0.04 M. The array density of grown ZnO nanorods per same area was increased with increasing the concentration of precursor solution. Vertically aligned ZnO nanorods with hexagonal wurtzite structure have highly preferred c-axis orientation along (002) lattice plane. Especially, ZnO nanorods array developed from 0.04 M precursor solution showed a diameter of about 85 nm and length of 1.2 {\mu}m$ without any crystallographic defects. The photoluminescence spectra of ZnO nanorods from heavier precursor concentration exhibited stronger UV emission around 380 nm corresponding with near-band-edge emission.

• Advances in nano research
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• 제1권1호
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• pp.59-70
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• 2013

ZnO nanostructures of rod-like, faceted bar, cup-end bars, and spindle shaped morphologies could be grown by a low power ultrasonic synthesis process. pH of the reaction mixture seems to plays an important role for defining the final morphology of ZnO nanostructures. While the solution pH as low as 7 produces long, uniform rod-like nanostructures of mixed phase (ZnO and $Zn(OH)_2$), higher pH of the reaction mixture produces ZnO nanostructures of different morphologies in pure hexagonal wurtzite phase. pH of the reaction as high as 10 produces bar shaped uniform nanostructures with lower specific surface area and lower surface and lattice defects, reducing the defect emissions of ZnO in the visible region of their photoluminescence spectra.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.119-119
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• 1999

GaN-based 물질들은 blue와 UV 영역의 LED, LD와 같은 광소자가 상용화되었을 뿐만아니라 HBT, FET와 같은 전기소자로도 널리 응용될 시점이지만 아직까지 해결되지 않은 문제점들이 있다. 그 중에 하나가 바로 GaN의 격자상수와 일치하는 기판이 없어 발생하는 dislocation인데, 이를 해결하기 위한 방법으로 새로운 기판이나, buffer, 또는 새로운 성장방법(ELOG) 등을 시도하고 있으나 dislocation density는 아직 높은 (107~1010cm-2) 상태이다. 이에 본 연구에서는 dislocation을 줄이기 위한 방책으로 InxGa1-xN를 새로운 buffer층으로 사용하여 GaN 박막을 MBE 방법으로 성장하였다. InxGa1-xN를 선택한 이유는 GaN와의 격자상수차이가 In0.12Ga0.88N일 경우 거의 일치한다는 보고가 있으며, 특히 InGaN의 melting point는 GaN의 성장온도 보다는 약간 높기 때문에 GaN 박막을 성장할 때와 식힐 때의 InGaN 원자결합은 약하게 작용되며, 결국 이는 열적인 stress를 줄여주게 된다. 이와 같이 성장된 GaN 박막은 그 결정성을 XRD로 분석하였고, 표면과 계면을 SEM으로 관찰하였다. 그리고 그 광학적 특성을 저온 PL로서 조사하였다. 그 결과를 살펴보면 35$^{\circ}$ 근방에서 GaN(0002) peak가 나온 것으로 보아 wurtzite 구조가 성장됨을 XRD로부터 확인하였다. 그리고 저온 (12K) PL에서는 3.470eV의 D$^{\circ}$X peak뿐만 아니라 3.258eV에 해당하는 peak를 얻었는데, 이는 InxGa1-xN buffer layer의 vapour pressure가 높은 (<50$0^{\circ}C$)에 도달하게 됨으로써 dissociation이 일어나면서 초기 성장이 이루어졌고 이는 다시 계면에서의 inter-diffusion을 발생시킨 것으로 보여진다.

• 한국세라믹학회지
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• 제50권3호
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• pp.173-179
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• 2013

Wurtzite nanomaterials, such as ZnO, GaN, and InN, have become a subject of great scientific and technological interest as they simultaneously have piezoelectric and semiconductor properties. In particular, the piezoelectric potential (piezopotential) created by dynamic straining in the nanowires drives a transient flow of current in the external load, converting mechanical energy into electricity. Further, the piezopotential can be used to control the carrier generation, transport, separation, and/or recombination at the metal-semiconductor junction or p-n junction, which is called the piezophototronic effect. This paper reviews the recent advances on the piezophototronic effect to better use the piezophototronic effect to control the carrier generation, transport, separation and/or recombination for improving the performance of optoelectronic devices, such as photon detectors, solar cells and LEDs. This paper also discusses several research and design studies that have improved the output performance of optoelectronic devices.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1645-1647
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• 1996

Polycrystalline CdTe thin films -have been studied for photovoltaic application because of their high absorption coefficient and optimal band gap energy (1.54 eV) for solar energy conversion. In this study, we prepared CdTe films using RF-magnetron sputtering method and investigated structural, optical and electrical properties with spectrophotometer, XRD, EDX, and resistivity meter. CdTe films at $200\;^{\circ}C$ showed a mixture of zinc blend (Cubic) and wurtzite (hexagonal) phase. On the other hand, the films at $400\;^{\circ}C$ showed highly oriented structure having hexagonal structure. The resistivity of CdTe films deposited on $SiO_2$ substrates was about $10_7\;{\Omega}cm$. The value of resistivity decreased with the increase of the substrate temperature. CdTe were sputtered on CdS thin films prepared by chemical bath deposition for the formation of the heterojunction. I-V characteristics of these cells were measured at a light density of $100mw/cm^2$, AM. 1.0. The present thin film solar cells showed a conversion efficiency of about 5%.

• Applied Science and Convergence Technology
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• 제23권6호
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• pp.376-386
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• 2014

Zinc oxysulfide nanocrystals (ZnOS NCs) were synthesized by forming ZnS phase on a ZnO matrix. ZnO nanocrystals (NCs) with a diameter of 10 nm were synthesized by forced hydrolysis in an organic solvent. As-synthesized ZnO NCs aggregated with each other due to the high surface energy. As acetic acid (AA) was added into the milky suspension of the aggregated ZnO NCs, transparent solution of well dispersed ZnO NCs formed. Finally ZnOS NCs were formed by adding thioacetic acid (TAA) to the transparent solution. The effect of recrystallization on the structural, optical and electrical properties of the ZnOS NCs were studied. The results of UV-vis absorption confirmed the band gap tunability caused by increasing the curing temperature of ZnOS thin films. This may have originated from the larger effective size due to the recrystallization of zinc sulfide (ZnS). From XRD result we identified that ZnOS thin films have a zinc blende crystal structure of ZnS without wurtzite ZnO structure. This is probably due to the small amount of ZnO phases. These assertions were verified through EDS of FE-SEM, XPS and EDS mapping of HR-TEM results; we clearly proved that ZnOS were comprised of ZnS and ZnO phases.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.289.2-289.2
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• 2014

본 연구에서는 전기증착법 정전류 방법으로 ITO 유리기판 위에 ZnO 나노막대를 성장하였다. 성장 매개 변수로 용액 농도, 전착 전류, 용액 온도 및 성장 시간으로 하였고, 성장된 ZnO 나노막대는 field-emission scanning electron microscopy, X-ray diffractometer, photoluminescence를 이용하여 구조적, 광학적 특성을 분석하였다. 모든 시료에서 ZnO 나노막대는 wurtzite 형태의 결정 구조를 가지고, c-축 배향성을 나타내는 강한 ZnO(002) 회절피크가 나타났다. 용액 농도와 전착 전류가 감소함에 따라 ZnO 나노막대의 밀도 및 직경이 감소하였다. 또한, ZnO 나노막대는 성장 온도가 증가함에 따라 직경이 줄어들었고, 성장 시간이 증가함에 따라 ZnO 나노막대의 길이는 늘어났다. 모든 ZnO 나노막대 시료는 자유 엑시톤 재결합에 의해서 3.18 eV, 산소공공에 의한 결함에 의해서 2.32~1.86 eV의 피크가 관찰되었다. ZnO 나노막대의 직경이 작아질수록 NBEE 피크의 세기가 감소하고, 용액의 농도가 증가함에 따라 NBEE 피크는 청색편이 하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.248.2-248.2
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• 2014

In this study, the optical properties and structural characteristics of gallium nitride (GaN) thin films prepared by radio frequency (RF) magnetron sputtering were investigated. Auger electron and X-ray photoelectron spectra showed that the deposited films consisted mainly of gallium and nitrogen. The presence of oxygen was also observed. The optical bandgap of the GaN films was measured to be approximately 3.31 eV. The value of the refractive index of the GaN films was found to be 2.36 at a wavelength of 633 nm. X-ray diffraction data revealed that the crystalline phase of the deposited GaN films changed from wurtzite to zinc-blende phase upon decreasing the sputtering gas pressure. Along with the phase change, a strong dependence of the microstructure of the GaN films on the sputtering gas pressure was also observed. The microstructure of the GaN films changed from a voided columnar structure having a rough surface to an extremely condensed structure with a very smooth surface morphology as the sputtering gas pressure was reduced. The relationship between the phase and microstructure changes in the GaN films will be discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.315.2-315.2
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• 2014

Pt-functionalized ZnS nanowires were synthesized on Au-deposited c-plane sapphire substrates by thermal evaporation of ZnS powders followed by wet Pt coating and annealing. The $NO_2$ gas sensing properties of multiple-networked Pt-functionalized ZnS nanowire sensors were examined. Scanning electron microscopy showed the nanowires with diameters of 20-80 nm. Transmission electron microscopy and X-ray diffraction showed that the nanowires were wurtzite-structured ZnS single crystals. The Pt-functionalized ZnS nanowire sensors showed enhanced sensing performance to $NO_2$ gas at $150^{\circ}C$ compared to pristine ZnS nanowire sensors. Pristine and Pt-functionalized ZnS nanowire sensors showed responses of 140-211% and 207-488%, respectively, to 1-5 ppm $NO_2$, which are better than or comparable to those of many oxide semiconductor sensors. In addition, the underlying mechanism of the enhancement of the sensing properties of ZnS nanowires by Pt functionalization is discussed.

• 한국재료학회지
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• 제27권10호
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• pp.530-533
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• 2017

ZnO micro/nanocrystals with different morphologies were synthesized by thermal evaporation of various zinc source materials in an air atmosphere. Zinc acetate, zinc carbonate and zinc iodide were used as the source materials. No catalysts or substrates were used in the synthesis of the ZnO crystals. The scanning electron microscope(SEM) image showed that the morphology of ZnO crystals was strongly dependent on the source materials, which suggests that source material is one of the key factors in controlling the morphology of the obtained ZnO crystals. Tetrapods, nanogranular shaped crystals, spherical particles and crayon-shaped crystals were obtained using different source materials. The X-ray diffraction(XRD) pattern revealed that the all the ZnO crystals had hexagonal wurtzite crystalline structures. An ultraviolet emission was observed in the cathodoluminescence spectrum of the ZnO crystals prepared via thermal evaporation of Zn powder. However, a strong green emission centered at around 500 nm was observed in the cathodoluminescence spectra of the ZnO crystals prepared using zinc salts as the source materials.