• 한국전기전자재료학회논문지
• /
• 제20권3호
• /
• pp.202-206
• /
• 2007

ZnO is a promising material to make high efficient ultraviolet(UV) or blue light emitting diodes(LEDs) because of its large binding energy and energy bandgap. In this study, we prepared ZnO thin films with p-type conductivity on silicon(100) substrates by RF magnetron sputtering in the mixture of $N_2$ and $O_2$. The process was accompanied by low pressure in-situ annealing in $O_2$ at $600^{\circ}C$ and $800^{\circ}C$ respectively. Hall effect in Van der Pauw configuration showed that the N-doped ZnO film annealed at $800^{\circ}C$ has p-type conductivity. Photoluminescence(PL) spectrum of the film annealed at $800^{\circ}C$ showed UV emission related to exciton and bound to donor-acceptor pair(DAP) as well as visible emission related to many intrinsic defects.

• 한국전기전자재료학회논문지
• /
• 제18권12호
• /
• pp.1087-1091
• /
• 2005

Four-probe device of single ZnO nanowire was fabricated by electron beam lithography. Electrical characterizations in a two-probe and a four-probe configuration with a back-gate were carried out to clarify the relative contribution of the contact and the intrinsic part in a ZnO nanowire. I-V characteristic in four-probe measurement showed an ohmic behavior with a high conductivity, 100 S/cm, which was better than those of two-probe measurement by 10 times. At the same values of the current between two-probe and four-probe, the net voltage applied inside the nanowire were extracted with calculated voltages at the contact. Four-probe current-gate voltage characteristics showed bigger tendencies than those of two-probe measurement at low temperatures, indicating the reduced gate dependence in two-Probe measurements by the existence of the contact resistance.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
• /
• pp.11-11
• /
• 2008

ZnO has a very large exciton binding energy (60 meV) as well as thermal and chemical stability, which are expected to allow efficient excitonic emission, even at room temperature. ZnO based electronic devices have attracted increasing interest as the backplanes for applications in the next-generation displays, such as active-matrix liquid crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs), and in solid state lighting systems as a substitution for GaN based light emitting diodes (LEDs). Most of these electronic devices employ the electrical behavior of n-type semiconducting active oxides due to the difficulty in obtaining a p-type film with long-term stability and high performance. p-type ZnO films can be produced by substituting group V elements (N, P, and As) for the O sites or group I elements (Li, Na, and K) for Zn sites. However, the achievement of p-type ZnO is a difficult task due to self-compensation induced from intrinsic donor defects, such as O vacancies (Vo) and Zn interstitials ($Zn_i$), or an unintentional extrinsic donor such as H. Phosphorus (P) doped ZnO thin films were grown on c-sapphire substrates by radio frequency magnetron sputtering with various Ar/ $O_2$ gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio with out post-annealing. The P-doped ZnO films grown at a Ar/ $O_2$ ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of $10^{-17}cm^{-3}$ and $2.5cm^2/V{\cdot}s$, respectively. X-ray diffraction showed that the ZnO (0002) peak shifted to lower angle due to the positioning of $p^{3-}$ ions with a smaller ionic radius in the $O^{2-}$ sites. This indicates that a p-type mechanism was due to the substitutional Po. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction LEO showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.

• Bulletin of the Korean Chemical Society
• /
• 제34권11호
• /
• pp.3301-3306
• /
• 2013

This paper aims to address the cellular toxicity of ultra-pure titanium dioxide ($TiO_2$) and zinc oxide (ZnO) nanoparticles (NPs) frequently employed in sunscreens as inorganic physical sun blockers to provide protection against adverse effects of ultraviolet (UV) radiation including UVB (290-320 nm) and UVA (320-400 nm). In consideration that the production and the use of inorganic NPs have aroused many concerns and controversies regarding their safety and toxicity and that microsized $TiO_2$ and ZnO have been increasingly replaced by $TiO_2$ and ZnO NPs (< 100 nm), it is very important to directly investigate a main problem related to the intrinsic/inherent toxicity of these NPs and/or their incompatibility with biological objects. In the present study, we took advantage of the laser-assisted method called laser ablation for generation of $TiO_2$ and ZnO NPs. NPs were prepared through a physical process of irradiating solid targets in liquid phase, enabling verification of the toxicity of ultra-pure NPs with nascent surfaces free from any contamination. Our results show that $TiO_2$ NPs are essentially non-poisonous and ZnO NPs are more toxic than $TiO_2$ NPs based on the cell viability assays.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.280.2-280.2
• /
• 2016

The graphene, a single atomic sheet of graphite, has attracted tremendous interest owing to its novel properties including high intrinsic mobility, optical transparency and flexibility. However, for more diverse application of graphene devices, it is essential to tune its transport behavior by shifting Dirac Point (DP) of graphene. So, in the following context, we suggest a method to tune structural and electronic properties of graphene using atomic layer deposition. By atomic layer deposition of zinc oxide (ZnO) on graphene using 4-mercaptophenol as linker, we can fabricate n-doped graphene. Through ${\pi}-{\pi}$ stacking between chemically inert graphene and 4-mercaptophenol, conformal deposition of ZnO on graphene was enabled. The electron mobility of graphene TFT increased more than 3 times without considerably decreasing the hole mobility, compared to the pristine graphene. Also, it has high air stability. This ZnO doping method by atomic layer deposition can be applicable to large scale array of CVD graphene TFT.

• 한국재료학회지
• /
• 제19권5호
• /
• pp.281-287
• /
• 2009

ZnO thin film was grown on a sapphire single crystal substrate by plasma assisted molecular beam epitaxy. In addition to near band edge (NBE) emissions, both blue and green luminescences are also observed together. The PL intensity of the blue luminescence (BL) range from 2.7 to 2.9 eV increased as the amount of activated oxygen increased, but green luminescence (GL) was weakly observed at about 2.4 eV without much change in intensity. This result is quite unlike previous studies in which BL and GL were regarded as the transition between shallow donor levels such as oxygen vacancy and interstitial zinc. Based on the transition level and formation energy of the ZnO intrinsic defects predicted through the first principle calculation, which employs density functional approximation (DFA) revised by local density approximation (LDA) and the LDA+U approach, the green and blue luminescence are nearly coincident with the transition from the conduction band to zinc vacancies of $V^{2-}_{Zn}$ and $V^-_{Zn}$, respectively.

• 한국결정성장학회지
• /
• 제11권2호
• /
• pp.49-55
• /
• 2001

sol-gel방법에 의해서 p-형 Si(100)웨이퍼와 ITO glass, quartz glass기판 위 ZnO박막을 형성시켰으며 출발 물질은 zinc acetate dihydrate를 사용하였다. Zinc acetate dihydrate를 2-methoxyethanol-monoethanolamine(MEA)용액에 녹여 :균질하고 안정된 용액을 만들었다. ZnO박막은 2800rpm에서 25초 동안 spin-coating하고 $250^{\circ}C$의 hot plate에서 10분 동안 중간 열처리한 후 이를 반복하여 형성시켰고 결정화를 위한 열처리는 $400^{\circ}C$~$800^{\circ}C$공기 분위기에서 1시간 동안 시행하였다. X-ray diffraction(XRD), scanning electron microscopy(SEM), UV-vis 투과 스펙트럼, IR 투과 스펙트럼, photoluminescence(PL)스펙트럼 등의 측정 결과로부터 박막의 구조적 특성과 광학적 성질에 대해서 논의하였다. 제조된 ZnO막은 (002)면으로 정렬되어 있으며 380nm파장에서 예리한 흡수단이 있고 가시광선 영역에서 투명(투과율 70% 이상)하였는데 이 흡수단은 ZnO의 밴드 갭(3.2eV)과 잘 일치한다. 저온에서의 띠끝 PL스펙트럼은 속박된 엑시톤 복합체와 포논 복제에 의한 다중선 구조를 보인다.

• 대한화학회지
• /
• 제28권4호
• /
• pp.251-258
• /
• 1984

색소를 흡착시킨 산화아연의 표면상태를 광기전력측정법을 이용하여 색소증감기구 및 바인더(binder)효과에 대한 연구를 수행하였다. 산화아연의 에너지트랩준위는 1.12eV이며, 색소흡착에 의해 0.99eV로 에너지준위가 낮아짐을 알았다. 바인더효과는 표면광기전력의 효율을 커지게 하나 에너지트랩준위에는 변화를 주지 않는다. 또한 색소증감기구로 흡착력이 강한 산형색소는 전자 이동(electron transfer)이며, 산화아연 고유흡수광에 減感작용이 있는 나트륨염형색소는 에너지이동(energy transfer)로써 추측된다. 근적외부인 1,100~1,350nm에 걸쳐 광기전력감도가 나타나므로 적외선에 의한 전자사진용 畵像材料로서 가능성을 제시하였다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1992년도 춘계학술대회 논문집
• /
• pp.97-100
• /
• 1992

The Degradation mechanism of the ZnO-varistor fabricated with the content of a 3-Composition seed grain is discussed using the method of Thermally Stimulated Current (TSC). The spectra of TSC is measured in the temperature range of -130～270$^{\circ}C$ with a various forming electric fields E$\sub$f/, temperature T$\sub$f/ time tf, and a various rising rate of temperature. It is observed that there are appeared the peaks of ${\alpha}$, ${\alpha}$$_2$, ${\beta}$ and ${\gamma}$from high temperature in a TSC spectrum. It seems that ${\alpha}$$_1$ peak is due to thermal depolarization of donor ions forming the space charge in the depletion layer, and ${\alpha}$$_2$peak is due to the detrapping of trapped electrons in deep trap level of intergranular layer, and ${\beta}$ peak is due to the thermal exciting of carrier existing in the donor level of grain itself, and ${\gamma}$ peak is due to the thermal exciting of trapped carrier in all shallow trap site randomly distributed in the inner of sample and/or a intrinsic impurity existing in it.

• 한국수소및신에너지학회논문집
• /
• 제13권3호
• /
• pp.214-223
• /
• 2002

Kinetic and effectiveness factors for methanol steam reforming using commercial copper-containing catalysts in a plug flow reactor were investigated over the temperature ranges of $180-250^{\circ}C$ at atmospheric pressure. The selectivity of $CO_2$/$H_2$ was almost 100%, and CO products were not observed under reaction conditions employed in this work. It was indicated that $CO_2$ was directly produced and CO was formed via the reverse water gas shift reaction after methanol steam reforming. The intrinsic kinetics for such reactions were well described by the Langmuir-Hinshelwood model based on the dual-site mechanism. The six parameters in this model, including the activation energy of 103kJ/mol, were estimated from diffusion-free data. The significant effect of internal diffusion was observed for temperature higher than $230^{\circ}C$ or particle sizes larger than 0.36mm. In the diflusion-limited case, this model combined with internal effectiveness factors was also found to be good agreement with experimental data.