• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 제4회 영호남학술대회 논문집
• /
• pp.84-91
• /
• 2002

The stochiometric composition of $AgGaS_2$/GaAs polycrystal source materials for the $AgGaS_2$/GaAs epilayer was prepared from horizontal furnace. From the extrapolation method of X-ray diffraction patterns it was found that the polycrystal $AgGaS_2$/GaAs has tetragonal structure of which lattice constant an and Co were 5.756 $\AA$ and 10.305 $\AA$, respectively. $AgGaS_2$/GaAs epilayer was deposited on throughly etched GaAs(100) substrate from mixed crystal $AgGaS_2$/GaAs by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $590^{\circ}C$ and $440^{\circ}C$ respectively. The crystallinity of the grown $AgGaS_2$/GaAs epilayer was investigated by the DCRC (double crystal X-ray diffraction rocking curve). The optical energy gaps were found to be 2.61 eV for $AgGaS_2$/GaAs epilayer at room temperature. The temperature dependence of the photocurrent peak energy is well explained by the Varshni equation, then the constants in the Varshni equation are given by $\alpha=8.695{\times}10^{-4}$ eV/K, and $\beta=332K$. From the photocurrent spectra by illumination of polarized light of the $AgGaS_2$/GaAs epilayer, we have found that crystal field splitting ${\Delta}Cr$ was 0.28 eV at 20 K. From the PL spectra at 20 K, the peaks corresponding to free and bound excitons and a broad emission band due to D-A pairs are identified. The binding energy of the free excitons are determined to be 0.2676 eV and 0.2430 eV and the dissociation energy of the bound excitons to be 0.4695 eV.

• 한국재료학회지
• /
• 제31권12호
• /
• pp.682-689
• /
• 2021

NbC, HfC, TaC, and their solid solution ceramics have been identified as the best materials for ultrahigh-temperature ceramics. However, their structural stability and elastic properties are mostly unclear. Thus, we investigated structure and elastic properties of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C solid solutions via ab initio calculations. Our calculated results show that the stability of (Nb_1-xTa_x)C and (Nb_1-xHf_x)C increases with the increase of Hf and Ta content, and (Nb_1-xHf_x)C is more stable than (Nb_1-xTa_x)C at the same content of Hf and Ta. The lattice constants decrease with increasing of Hf and Ta content. (Nb_1-xTa_x)C and (Nb_1-xHf_x)C carbides are mechanically stable and brittle. Bulk modulus of (Nb_1-xTa_x)C increases with increasing Ta content. In contrast, bulk modulus of (Nb_1-xHf_x)C decreases with increasing Hf content. Hardness of solid solutions shows the highest values at the (Nb_0.25Ta_0.75)C and (Nb_0.75Hf_0.25)C. In particular, (Nb_0.75Hf_0.25)C shows the highest hardness for the current system. The results indicate that the overall mechanical properties of (Nb_1-xHf_x)C solid solutions are superior to those of (Nb_1-xTa_x)C solid solutions. Therefore, controlling the Hf and Ta element and content of the (Nb_1-xTa_x)C and (Nb_1-xHf_x)C Solid solution is crucial for optimizing the material properties.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
• /
• pp.81-81
• /
• 2003

The stochiometric mixture of evaporating materials for the CuGaSe$_2$ single crystal thin films were prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal CuGaSe$_2$, it was found tetragonal structure whose lattice constant no and co were 5.615$\AA$ and 11.025$\AA$, respectively. To obtains the single crystal thin films, CuGaSe$_2$ mixed crystal was deposited on throughly etched GaAs(100) by the Hot Wall Epitaxy(HWE) system. The source and substrate temperature were 61$0^{\circ}C$ and 45$0^{\circ}C$ respectively, and the growth rate of the single crystal thin films was about 0.5${\mu}{\textrm}{m}$/h. The crystalline structure of single crystal thin films was investigated by the double crystal X-ray diffraction(DCXD). Hall effect on this sample was measured by the method of van der pauw and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by pizoelectric scattering in the temperature range 30K to 150K and by polar optical scattering in the temperature range 150K to 293K. The optical energy gaps were found to be 1.68eV for CuGaSe$_2$ single crystal thin films at room temperature. The temperature dependence of the photocurrent peak energy is well explained by the Varshni equation then the constants in the Varshni equation are given by a=9.615$\times$ 10$^{-4}$ eV/K, and $\beta$=335K. From the photocurrent spectra by illumination of polarized light of the CuGaSe$_2$ single crystal thin films. We have found that values of spin orbit coupling ΔSo and crystal field splitting ΔCr was 0.0900eV and 0.2498eV, respectively. From the PL spectra at 20K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0626eV and the dissipation energy of the acceptor-bound exciton and donor-bound exciton to be 0.0352eV, 0.0932eV, respectively.

• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
• /
• pp.75-87
• /
• 1996

This review is presented under the following headings: 1.Introduction 1.1 Brief review of the properties of AlN 1.2 Historical survey of work on ceramic and single crystal AlN 2.Thermochemical background 3.Crystal growth 4.Doping 5.Potential applications and future work The known properties of AlN which make it of interest for various are discussed briefly. The properties include chemical stability, crystal structure and lattice constants, refractive indices and other optical properties, dielectric constant, surface acoustic wave velocity and thermal conductivity. The history of work in single crystals, thin films and ceramics are outlined and the thermochemistry of AlN reviewed together with some of the relevant properties of aluminium and nitrogen; the problems encountered in growing crystals of AlN are shown to arise directly from these thermochemical relationships. Methods have been reported in the literature for growing AlN crystals from melts, solution and vapour and these methods are compared critically. It is proposed that the only practicable approach to the growth of AlN is by vapour phase methods. All vapour based procedures share the share the same problems: $.$the difficulty of preventing contamination by oxygen & carbon $.$the high bond energy of molecular nitrogen $.$the refractory nature of AlN (melting point~3073K at 100ats.) $.$the high reactivity of Al at high temperatures It is shown that the growth of epitactic layers and polycrystalline layers present additional problems: $.$chemical incompatibility of substrates $.$crystallographic mismatch of substrates $.$thermal mismatch of substrates The result of all these problems is that there is no good substrate material for the growth of AlN layers. Organometallic precursors which contain an Al-N bond have been used recently to deposit AlN layers but organometallic precursors gave the disadvantage of giving significant carbon contamination. Organometallic precursors which contain an Al-N bound have been used recently to deposit AlN layers but organometallic precursors have the disadvantage of giving significant carbon contamination. It is conclude that progress in the application of AlN to optical and electronic devices will be made only if considerable effort is devoted to the growth of larges, pure (and particularly, oxygen-free) crystals. Progress in applications of epi-layers and ceramic AlN would almost certainly be assisted also by the availability of more reliable data on the pure material. The essential features of any stategy for the growth of AlN from the vapour are outlined and discussed.

• 자원환경지질
• /
• 제56권1호
• /
• pp.13-21
• /
• 2023

합성 제올라이트 X의 고온 고압 하에서 압력 전달 매개체에 따른 체적탄성계수와 상전이 특성을 이해하기 위해 X-선 분말 회절 연구를 진행하였다. 제올라이트 X에 물과 탄산 용액을 압력전달매개체로 사용하여 상온 상압에서 최대 250 ℃, 5.18 GPa까지 가열 및 가압하는 과정에서 나타나는 단위포 부피 변화와 상전이를 방사광 X-선 회절을 통해 관찰하였다. 르바일의 전체 분말 패턴 분해법이 적용된 GSAS2 프로그램을 사용하여 각 압력 단계에서 제올라이트 X와 그멜리나이트, 나트로라이트, 스멕타이트의 격자상수와 단위포 부피를 도출하였다. 버치-머내한 2차 방정식이 적용된 EosFIt 프로그램을 사용하여 각 제올라이트 X와 스멕타이트의 체적탄성계수를 구하였다. 물을 사용한 실험에서 제올라이트 X의 체적탄성계수는 89(3) GPa, 탄산 수용액을 사용한 실험에서 제올라이트 X의 체적탄성계수는 92(3) GPa이다. 두 실험 모두 최초 가압 시 제올라이트 X 내부로 압력 전달 매개체의 유입으로 인한 부피 증가 현상이 발생하였다. 물을 사용한 실험에서 제올라이트 X는 그멜리나이트, 나트로라이트, 스멕타이트로 상전이 하였으며, 탄산 수용액을 사용한 실험에서 제올라이트 X는 스멕타이트로 상전이 하였다. 물을 사용한 실험에서 나타난 제올라이트 간 변화는 탄산 수용액을 사용한 실험에서는 발생하지 않았으며, 이는 특정 제올라이트 생성 조건이 압력 전달 매개체 pH와 연관이 있는 것으로 판단된다.

• 한국자기학회지
• /
• 제14권1호
• /
• pp.46-50
• /
• 2004

자성 garnet $Y_3$F $e_{5}$ $O_{12}$의 Y자리에 Ce이 치환된 $Y_{3-x}$C $e_{x}$F $e_{5}$ $O_{12}$(x=0.0, 0.1, 0.2, 0.3) 분말을 졸-겔법으로 합성하였다. $Y_{3-x}$C $e_{x}$F $e_{5}$ $O_{12}$의 결정학적 자기적 성질을 X-선 회절기(XRD), 진동시료 자화율 측정기(VSM)및 Mossbauer분광기를 이용하여 연구하였다. $Y_{3-x}$C $e_{x}$F $e_{5}$ $O_{12}$의 결정구조는 cubic이며, 격자상수는 x = 0.0에서 0.3까지 치환하였을 때 12.3758 $\pm$ 0.0005 $\AA$부터 12.4062 $\pm$ 0.0005 $\AA$으로 선형적으로 증가함을 보였다. VSM 측정 결과 $Y_{3-x}$C $e_{x}$F $e_{5}$ $O_{12}$의 포화 자화(saturation magnetization) 값은 거의 변화가 없었던 반면, 보자력(coercivity) 값은 $Y_3$F $e_{5}$ $O_{12}$과 $Y_{2.9}$C $e_{0.1}$F $e_{5}$ $O_{12}$일때 각각 18.3 Oe에서 5.8 Oe로 감소하였다. 이들 시료의 Mossbauer spectrum을 13K부터 Neel온도까지 측정을 하였다. Fe원자 위치의 분포를 고려하여 16a와 24d에 site의 2set으로 분석하였으며, 또한 $Y_{3-x}$C $e_{x}$F $e_{5}$ $O_{12}$의 자성 이온간의 상호작용을 Neel 이론으로 해석할 수 있었으며 개별 부격자간의 초교환 상호작용의 세기를 결정하였다. Debye 온도를 분석 결과 24d site 의 고체의 굳기가 16a site 경우보다 더 큰 것으로 분석 되었다.te 의 고체의 굳기가 16a site 경우보다 더 큰 것으로 분석 되었다.다. 분석 되었다.다.

• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
• /
• pp.258-292
• /
• 1996

In the last year great interest appears to YBCO thin films preparation on different substrate materials. Preparation of epitaxial film is a very difficult problem. There are many requirements to substrate materials that must be fullfilled. Main problems are lattice mismatch (misfit) and similarity of structure. From paper [1] or follows that difference in interatomic distances and angles of substrate and film is mire important problem than similarity of structure. In this work we present interatomic distances and angle relations between substrate materials belonging to ABCO4 group (where A-Sr or Ca, B-rare earth element, C-Al or Ga) of different orientations and YBCO thin films. There are many materials used as substrates for HTsC thin films. ABCO4 group of compounds is characterized by small dielectric constants (it is necessary for microwave applications of HTsC films), absence of twins and small misfit [2]. There most interesting compounds CaNdAlO4, SrLaAlO4 and SrLaGaO4 were investigated. All these compounds are of pseudo-perovskite structure with space group 14/mmm. This structure is very similar to structure of YBCO. SLG substrate has the lowest misfit (0.3%) and dielectric constant. For preparation of then films of substrates of this group of compound plane of <100> orientation are mainly used. Good quality films of <001> orientations are obtained [3]. In this case not only a-a misfit play role, but c-3b misfit is very important too. Sometimes, for preparation of thin films substrates of <001> and <110> orientations were manufactured [3]. Different misfits for different YBCO faces have been analyzed. It has been found that the mismatching factor for (100) face is very similar to that for (001) face so there is possibility of preparation of thin films on both orientations. SrLaAlO4(SLA) and SrLaGaO4(SLG) crystals of general formula ABCO4 have been grown by the Czochralski method. The quality of SLA and SLG crystals strongly depends on axial gradient of temperature and growth and rotation rates. High quality crystals were obtained at axial gradient of temperature near crystal-melt interface lower than 50℃/cm, growth rate 1-3 mm/h and the rotation rate changing from 10-20pm[4]. Strong anisotropy in morphology of SLA and SLG single crystals grown by the Czochralski method is clearly visible. On the basics of our considerations for ABCO4 type of the tetragonal crystals there can appear {001}, {101}, and {110} faces for ionic type model [5]. Morphology of these crystals depend on ionic-covalent character of bonding and crystal growth parameters. Point defects are observed in crystals and they are reflected in color changes (colorless, yellow, green). Point defects are detected in directions perpendicular to oxide planes and are connected with instability of oxygen position in lattice. To investigate facets formations crystals were doped with Cr3+, Er3+, Pr3+, Ba2+. Chromium greater size ion which is substituted for Al3+ clearly induces faceting. There appear easy {110} faces and SLA crystals crack even then the amount of Cr is below 0.3at.% SLG single crystals are not so sensitive to the content of chromium ions. It was also found that if {110} face appears at the beginning of growth process the crystal changes its color on the plane {110} but it happens only on the shoulder part. The projection of {110} face has a great amount of oxygen positions which can be easy defected. Pure and doped SLA and SLG crystals measured by EPR in the<110> direction show more intensive lines than in other directions which allows to suggest that the amount of oxygen defects on the {110} plane is higher. In order to find the origin of colors and their relation with the crystal stability, a set of SLA and SLG crystals were investigated using optical spectroscopy. The colored samples exhibit an absorption band stretching from the UV absorption edge of the crystal, from about 240 nm to about 550 m. In the case of colorless sample, the absorption spectrum consists of a relatively weak band in the UV region. The spectral position and intensities of absorption bands of SLA are typical for imperfection similar to color centers which may be created in most of oxide crystals by UV and X-radiation. It is pointed out that crystal growth process of polycomponent oxide crystals by Czochralski method depends on the preparation of melt and its stoichiometry, orientation of seed, gradient of temperature at crystal-melt interface, parameters of growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth. Growth parameters have an influence on the morphology of crystal-melt interface, type and concentration of defects.

• 한국진공학회지
• /
• 제6권2호
• /
• pp.129-135
• /
• 1997

$ZnIn_2Se_4$ 및 $ZnIn_2Se_4$:Co 단결정을 합성된 ingot를 사용하여 수직 Bridgman 방법으 로 성장시키고, 성장된 단결정의 결정구조와 광학적 특성을 연구하였다. 성장된 단결정은 공 간군이 142m인 사방정계구조를 가지고 있다. 기초 흡수단 영역에서의 광흡수 spectra측정으 로부터 이 단결정들은 간접전이형 에너지띠 구조를 갖고 있으며, 이 화합물 반도체의 직접 전이형 및 간접전이형 에너지 간격은 10K에서 300K로 측정 온도를 변화시킬 때 감소하였 다. 직접전이 energy gap의 온도계수는 $ZnIn_2Se_4$ 단결정의 경우는 $\alpha=3.57\times10^{-4}$eV/K, $\beta$ =519K이고, $ZnIn_2Se_4$:Co 단결정의 경우는 $\alpha=2.79\times10^{-4}$eV/K 및 $\beta$=421K로 각각 주어졌다. 또한 간접전이 energy gap의 온도계수는 ZnIn2Se4 단결정의 경우는 $\alpha=2.31\times10^{-4}$eV/K 및 $\beta$=285K이며, $ZnIn_2Se_4$:Co 단결정의 경우는 $\alpha=3.71\times10^{-4}$eV:K와 $\beta$=609K이였다. $ZnIn_2Se_4$:Co 단결정에서 cobalt 불순물에 기인한 6개의 불순물 광흡수 peak가 나타났다. 이 들 불순물 광흡수 peak들은 불순물로 첨가된 cobalt가 모체별정의 $T_d$ symmetry site에 $CO^{2+}$ion으로 위치하고, $CO^{2+}$ion의 분리된 전자에너지 준위들 사이의 전자전이에 의해 나타난 peak들로 해석된다.

• 한국결정성장학회지
• /
• 제21권3호
• /
• pp.99-104
• /
• 2011

단결정 성장을 위한 $MgGa_2Se_4$ 다결정은 수평 전기로에서 합성하였으며, 결정구조는 rhombohedral이고 격자상수 $a_0$는 3.953 ${\AA}$, $c_0$는 38.890 ${\AA}$였다. $MgGa_2Se_4$ 단결정박막은 HWE(Hot Wall Epitaxy) 방법으로 반절연성 GaAs(100)기판에 성장시켰다. 단결정박막의 성장 조건은 증발원의 온도 $610^{\circ}C$, 기판의 온도 $400^{\circ}C$에서 진행되었으며 성장 속도는 0.5 ${\mu}m/h$였다. 단결정박막의 결정성은 이중 결정 x-선 회절곡선의 반폭치와 X-선 회절무늬의 ${\omega}-2{\theta}$로부터 구하여 최적 성장 조건을 알 수 있었다. Hall 효과는 van der Pauw 방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293 K에서 각각 $6.21{\times}10^{18}/cm^3$, 248 $cm^2/v{\cdot}s$였다. $MgGa_2Se_4$/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수 스펙트럼을 10 K에서 293 K까지 측정하였다. 광흡수 스펙트럼으로부터 구한 에너지 갭 $E_g(T)$는 varshni 공식 $E_g(T)=E_g(0)=({\alpha}T^2/T+{\beta})$을 잘 만족함을 알 수 있었다. 여기서 $E_g(0)=2.34\;eV$, ${\alpha}=8.81{\times}10^{-4}\;eV/K$, ${\beta}=251\;K$였다.

• 한국자기학회지
• /
• 제18권2호
• /
• pp.67-70
• /
• 2008

$Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1)의 조성을 가지는 분말 시료를 sol-gel 법과 진공봉합 열처리를 이용하여 합성하였다. x선 회절기, $M\ddot{o}ssbauer$ 분광기를 이용하여 시료의 결정구조 및 Ga 이온의 점유도에 관하여 연구하였다. XRD측정결과 $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$ (x=0, 1)의 결정구조는 Ia3d의 공간그룹을 갖는 cubic 구조이며, $Tb_2Bi_1Fe_5O_{12}$와 $Tb_2Bi_1Ga_1Fe_4O_{12}$의 격자상수 $a_0$는 각각 $12.497\AA$, $12.465\AA$으로 분석되었다. Rietveld 분석법을 이용하여 각 이온들이 점유하는 각각의 부격자 위치를 연구하였다. $Tb_2Bi_1Ga_1Fe_4O_{12}$ 시료의 분석결과, Tb, Bi 이온은 24c 자리에, Fe 이온은 24d, 16a 자리를 점유하였으며, 비자성 이온인 Ga 이온은 모두 16a 자리를 점유하는 것으로 분석되었다. $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1)의 미시적인 자기구조를 분석하기 위해 시료들의 $M\ddot{o}ssbauer$스펙트럼을 측정하였다. 상온에서의 $M\ddot{o}ssbauer$스펙트럼 측정결과 철 이온들의 흡수 면적비는 $Tb_2Bi_1Fe_5O_{12}$의 경우 24d와 16a자리에서 각각 60.8%, 39.2%로, $Tb_2Bi_1Ga_1Fe_4O_{12}$의 경우 24d와 16a자리에서 각각 74.7%, 25.3%로 분석되었다. 철 이온들의 흡수 면적비 분석을 통해 비자성이온인 Ga은 모두 16a 자리를 점유하는 것을 알 수 있었다.