• 한국세라믹학회지
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• 제53권3호
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• pp.301-305
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• 2016

We investigate proton conduction in a nonstoichiometric ${\Sigma}3$ $BaZrO_3$ (210)[001] tilt grain boundary using density functional theory (DFT). We employ the space charge layer (SCL) and structural disorder (SD) models with the introduction of protons and oxygen vacancies into the system. The segregation energies of proton and oxygen vacancy are determined as -0.70 and -0.54 eV, respectively. Based on this data, we obtain a Schottky barrier height of 0.52 V and defect concentrations at 600K, in agreement with the reported experimental values. We calculate the energy barrier for proton migration across the grain boundary core as 0.61 eV, from which we derive proton mobility. We also obtain the proton conductivity from the knowledge of proton concentration and mobility. We find that the calculated conductivity of the nonstoichiometric grain boundary is similar to those of the stoichiometric ones in the literature.

• ETRI Journal
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• 제11권4호
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• pp.75-83
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• 1989

The diffusion mechanism of Si in GaAs was investigated using different diffusion sources based on the Si-Ga-As ternary phase equilibria. The Si profiles are measured with secondary ion mass spectrometry and differ significantly for sources taken from the different phase fields in the ternary phase diagram. Neutral As vacancy diffusion is proposed for acceptor Si diffusion anneals using a Ga - Si - GaAs source. Donor Si diffusion using As - rich sources and a Si -GaAs tie line source shows concentration dependent diffusion behavior. Concentration dependent diffusion coefficients of donor Si for As - rich source diffusion were found to be related to net ionized donor concentration and showed three regimes of different behavior: saturation regime, intermediate regime,and intrinsic regime. Ga vacancies are proposed to be responsible for donor Si diffusionin GaAs: $Si_Ga^+V_Ga^-$ (donor Si -acceptor Gavacancy) complex for the extrinsic regime and neutral $V_G$a, for the intrinsic regime.The Si - GaAs tie line source resulted in two branch profiles, intermediate between the As - rich and the Ga - rich source diffusion cases.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.306-306
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• 2011

Three dimensional(3D) topological insulators(TIs) of Bi binary alloys are characterized by a bulk energy gap with strong spin-orbit coupling and metallic surface states protected by time-reversal symmetry. It was reported that film forms of such materials were advantageous over bulk forms due to less defect density and better crystallinity. So far, the films have been prepared on several substrates including semiconductors and graphene. But, there were no studies on metal substrates. For electronic transport experiments and device applications, it is necessary to know epitaxial relation between TIs and metal electrodes. In this study, Atomically flat films of Bi2Se3 were grown on a Au(111) metal substrate by in-situ molecular beam epitaxy. Using home-built scanning tunneling microscope, we observed hexagonal atomic structures which corresponded to the outmost selenium atomic layer of Bi2Se3. Triangular-shaped defects known as Selenium vacancy were also found.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.61-61
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• 2011

Using ab initio calculations, we study the MgO(001) and Fe/MgO(001) surface phases and the effects of interface structure on the Fe/MgO magnetic anisotropy. The surface phase diagrams of MgO(001) and Fe/MgO(001) show that the most stable surface structures are either defect-free surface or the surfaces with oxygen vacancies in c($2{\times}1$) periodicity for the systems. By the formations of the oxygen vacancy rows on MgO(001) surface, the in-plane magnetic anisotropy energy of Fe overlayer is reduced while the perpendicular magnetic anisotropy energy is increased from 0.1 to 0.5 meV per Fe atom.

• 한국세라믹학회지
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• 제37권8호
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• pp.799-804
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• 2000

Coulometric titration experiments have been done for copper doped cobaltous oxide (Co1-xCux)1-$\delta$ O with various dopant concentrations. We present the obtained experimental data and compare our results to those of previous thermogravimetric investigation. The experimental data are fitted by theoretical calculations based on various defect models. For this modeling, we considered different types fo major defects like copper in substitutional and interstitial lattice sites as well as copper vacancy. We also introduced the copper evaporation effect during titration experiment into our consideration.

• 한국전기전자재료학회논문지
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• 제24권12호
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• pp.962-968
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• 2011

In this study, we investigated the effects of Mn dopant (0.1~3.0 at% $Mn_3O_4$ sintered at 1000$^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and grain boundary properties of ZnO, ZM(0.1~3.0) using admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). As a result, three kinds of defect were found below the conduction band edge of ZnO as 0.09~0.14 eV (attractive coulombic center), 0.22~25 eV ($Zn^{{\cdot}{\cdot}}_i$), and 0.32~0.33 eV ($V^{\cdot}_o$). The oxygen vacancy increased with Mn doping. In ZM, an electrically single grain boundary as double Schottky barrier was formed with 0.82~1.0 eV of activation energies by IS & MS. We also find out that the barriers of grain boundary of Mn-doped ZnO (${\alpha}$-factor=0.13) were more stabilized and homogenized with temperature compared to pure ZnO.

• 한국재료학회지
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• 제11권1호
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• pp.55-60
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• 2001

고 에너지 (1.5 MeV) 이온 주입된 Boron의 농도와 silicon 기판의 초기 산소 농도의 변화에 따라 silicon기판에 형성된 결정 결함 및 금속 불순물의 Gettering 효율에 대하여 DLTS(Deep Level Transient Spectroscopy), SIMS(Secondary ion Mass Spectroscopy), BMD(Bulk Micro-Defect) analysis 및 TEM (Transmission Electron Microscopy)을 이용하여 연구하였다. 이온 주입 전후의 DLTS 결과를 확산로 및 RTA를 이용한 열처리 전후의 DLTS 결과와 비교할 때 이온 주입 전 시편에서 볼 수 있는 공공에 의한 깊은 준위는 열처리 온도의 증가에 따라 금속 불순물과 관련된 깊은 준위로 천이함을 알 수 있다. 또한 고온 열처리의 경우, 초기 산소 농도가 높을수록 깊은 준위의 농도가 감소함을 볼 때 초기 산소 농도가 높을 수록 gettering 효율 측면에서 유리한 것으로 사료된다

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.187-207
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• 1999

The thermal distributions near the growth interface of 150mm CZ crystals were measured by three thermocouples installed at the center, middle (half radius) and edge (10m from surface) of the crystals. The results show that larger growth rates produced smaller thermal gradients. This contradicts the widely used heat flux balance equation. Using this fact, it si confirmed in CZ crystals that the type of point defects created is determined by the value of the thermal gradient (G) near the interface during growth, as already reported for FZ crystals. Although depending on the growth systems the effective lengths of the thermal gradient for defect generation are varied, were defined the effective length as 10mm from the interface in this experiment. If the G is roughly smaller than 20C/cm, vacancy rich CZ crystals are produced. If G is larger than 25C/cm, the species of point defects changes dramatically from vacancies to interstitial. The experimental results which FZ and CZ crystals are detached from the melt show that growth interfaces are filled with vacancy. We propose that large G produces shrunk lattice spacing and in order to relax such lattice excess interstitial are necessary. Such interstitial recombine with vacancies which were generated at the growth interface, next occupy interstitial sites and residuals aggregate themselves to make stacking faults and dislocation loops during cooling. The shape of the growth interface is also determined by the distributions of G across the interface. That is, the small G and the large G in the center induce concave and convex interfaces to the melt, respectively.

• 한국재료학회지
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• 제31권6호
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• pp.320-324
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• 2021

Effects of growth variables and post-growth annealing on the optical, structural and electrical properties of magnetron-sputtered Ga_0.04Mg_0.10Zn_0.86O films are characterized in detail. It is observed that films grown from pure oxygen plasma showed high resistivity, ~10² Ω·cm, whereas films grown in Ar plasma showed much lower resistivity, 2.0 × 10^-2 ~ 1.0 × 10^-1 Ω·cm. Post-growth annealing significantly improved the electrical resistivity, to 4.3 ~ 9.0 × 10^-3 Ω·cm for the vacuum annealed samples and to 1.3 ~ 3.0 × 10^-3 Ω·cm for the films annealed in Zn vapor. It is proposed that these phenomena may be attributed to the improved crystalline quality and to changes in the defect chemistry. It is suggested that growth within oxygen environments leads to suppression of oxygen vacancy (Vo) donors and formation of Zn vacancy (V_Zn) acceptors, resulting in highly resistive films. After annealing treatment, the activation of Ga donors is enhanced, Vo donors are annihilated, and crystalline quality is improved, increasing the electron mobility and the concentration. After annealing in Zn vapor, Zn interstitial donors are introduced, further increasing the electron concentration.

• 한국결정성장학회지
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• 제6권3호
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• pp.327-340
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• 1996

고주파로의 이용한 Czocharalski 법으로 congruent$(R_{m}=R_{c}=0.945)$, stoichiometric$(R_{m}=1,\;R_{c}=0.957)$, Li-rich$(R_{m}=1.202,\;R_{c}=0.989)$, congruent한 조성에 $K_{2}O$를 6 wt% 첨가한 $LiNbO_{3}$ 등의 순수한 단결정들과 congruent한 조성에 Mg와 Mn을 불순물로 첨가한 $LiNbO_{3}:Mn(0.1\;mole%),\;LiNbO_{3}:Mg(4.5,\;6.0,\;10.0\;mole%),\;LiNbO_{3}:(Mg(4.5,\;6.0,\;10.0\;mole%)+Mn(0.1\;mole%))$ 단결정들을 결정의 c.축 방향으로 성장시켰다. 실온데서 UV 스펙트럼과 IR 스펙트럼을 측정한 결과 UV 흡수단과 $OH^{-}$ 흡수 스펙트럼은 [Li]/[Nb] 비에 따라 변화한다. 또 첨가한 Mg, Mn 불순물들의 영향을 받는데 UV 흡수단의 위치와 $OH^{-}$ 흡수 스펙트럼의 위치, 모양이 Mg의 첨가량에 크게 의존하며 이는 Mg의 첨가량에 따라 이 이온의 결정내 위치가 달라지기 때문이다. 순수한 단별정들에 대한 $OH^{-}$ 흡수 스펙트럼을 Gaussian 선모습 함수를 써서 3, 5 개의 성분 스펙트럼으로 분해한다. 이 결과를 설명하기 위한 $LiNbO_{3}$ 단결정내의 배내, 배외 결함 구조에 대한 논의로 부터 Li 빈자리 모델이 결함 구조를 설명하는데 적합하다는 결론을 내렸고 이들 불순물 이온의 결정내의 위치도 정한다. 또한 결함 구조에 대한 본 연구의 결론을 이용하여 최근의 다른 연구자들의 실험 결과도 설명한다.