• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.278-281
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• 2011

The optical band gap energy for $SrTiO_3$ by reduction at high temperature was 3.15 eV. The reflectivity of reduced $SrTiO_3$ single crystals showed little variation, however, the reflectivity by the reduction condition had no effect. For the phonon mode at about 790 $cm^{-1}$, a blue-shift took place upon $N_2$ reduction and the decreased. However, a red-shift took place upon a $H_2-N_2$ reduction and the increased at the same phonon mode. With decreasing temperature the dielectric constant decreased rapidly. The thermal activation energies were 0.92-1.02 eV.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.94-97
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• 2002

CdS and $CdS:Co^{2+}$ single crystals were grown by CTR method using iodine as transport material. The grown single crystals have defect chalcopyrite structure with direct band gap. The optical energy band gap was decreased according to add of Co-impurity. We can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_d$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.67.1-67.1
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• 2010

Triple junction solar cell을 위한 a-SiGe middle cell의 조건별 광학적 특성에 관한 연구를 실시하였다. a-SiGe I층은 GeH4 유량, 압력, H2 dilution ratio를 변화시켜 제조하였으며 전기적, 광학적 특성을 비교하여 최종적으로 선택된 조건을 triple junction solar cell에 적용하였다. a-SiGe I층은 Ge contents가 증가함에 따라 band gap은 감소하고 45% 이상의 조건에서는 700nm 전후 파장의 투과율이 감소하며, 압력이 감소함에 따라 band gap은 소폭 감소하나 700nm 전후 파장의 투과율은 증가하였다. 그리고 H2 ratio가 증가함에 따라 band gap은 소폭 감소하나 투과율에는 큰 변화가 없었다. 상기 결과를 바탕으로 최종적으로 선택된 조건에서 triple-junction solar cell을 제작하여 평가한 결과 초기 변환효율 9%의 결과를 얻었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.426-426
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• 2008

ZnO 박막과 Al이 도핑된 ZnO 다결정질 박막을 rf magnetron sputtering 방법을 이용하여 Si(100) 기판과 코닝글라스 기판에 증착하여 박막의 광학적 특성을 Spectro-scopic Ellipsometry (SE, Woollam사)와 UV-VIR-NIR Sphectrophotometry (SP, Varian사)를 사용하여 분석하였다. SE 측정은 입사각도 55도에서 75도까지 5도 간격으로 파장범위 250 - 1700 nm 에서 3 nm 간격으로 측정하였으며, SP 측정은 수직입사로 250-3000 nm 파장범위에서 1 nm 간격으로 투과도와 반사도를 측정하였다. 측정된 데이터들은 Lorentz Oscillator 모델과 Drude free electron 모델이 결합된 분산관계식을 사용하여 전산 맞춤을 하여 분석하였다. ZnO 박막의 optical band gap energy 는 3.3 eV로 측정되었으며, Al 도핑에 따른 자유전하농도가 증가에 의하여 Burstein-Moss 효과에 따르는 optical band gap energy의 증가 거동을 보였다. 또한 자유전하농도 증가에 따라 band edge 부근에서 나타나는 excitonic transition 에 기인하는 유전함수 피크의 broadening이 관찰되었으며, high frequency dielectric constant는 자유 전하농도에 관계없이 3.689${\pm}$0.05 eV 의 값을 가졌다. Drude free electron 모델을 사용하여 plasma frequency를 구하고 이로부터 얻어진 optical mobility 와 Hall mobility를 비교하여 ZnO계 다결정질 박막에서의 결정립계가 이동도에 미치는 영향을 고찰하고자 한다.

• Korean Journal of Materials Research
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• v.32 no.5
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• pp.249-257
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• 2022

Transparent thin films of pure and nickel-doped ZrO₂ are grown successfully by sol-gel dip-coating technique. The structural and optical properties according to the different annealing temperatures (300 ℃, 400 ℃ and 500 ℃) are investigated. Analysis of crystallographic properties through X-ray diffraction pattern reveals an increase in crystallite size due to increase in crystallinity with temperature. All fabricated thin films are highly-oriented along (101) planes, which enhances the increase in nickel doping. Scanning electron microscopy and energy dispersive spectroscopy are employed to confirm the homogeneity in surface morphology as well as the doping configuration of films. The extinction coefficient is found to be on the order of 10^-2, showing the surface smoothness of deposited thin films. UV-visible spectroscopy reveals a decrease in the optical band gap with the increase in annealing temperature due to the increase in crystallite size. The variation in Urbach energy and defect density with doping and the change in annealing temperature are also studied.

• Electrical & Electronic Materials
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• v.10 no.2
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• pp.105-112
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• 1997

Undoped and Co$^{2+}$-doped Zn$_{4}$GeSe$_{6}$ single crystals were grown by the Chemical Transport Reaction method using iodine as a transporting agent. The crystal structure of these compounds determined by X-ray diffraction analysis was monoclinic structure. The direct energy gaps of these compounds were measured and the temperature dependence of the optical energy gap were closely investigated over the temperature range 10-290K. The temperature dependence of the optical energy gap is well presented by the Varshni equation. Also the optical absorption peaks of Zn$_{4}$GeSe$_{6}$ :Co$^{2+}$ single crystal observed, centered at 5437, 6079, 7142, 12950, 13462, 14786 and 15735 $cm^{-1}$ /, can be explained in terms of the electronic transitions of Co$^{2+}$ ions located at Td symmetry of the host materials. According to the crystal-field theory, the crystal-field, Racah and spin-orbit coupling parameters obtained from the absorption bands are given by Dq = 361$cm^{-1}$ /, B = 655$cm^{-1}$ / and .lambda. = 284$cm^{-1}$ / respectively.ively.

• New & Renewable Energy
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• v.3 no.4
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• pp.54-62
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• 2007

In this paper, we report the research highlight on the preparation and characterization of Indium-free $Cu_2ZnSnSe_4$ and Indium-reduced $CulnZnSe_2$ thin films in order to seek the viability of these absorber materials to be applied in thin film solar cells. The films of $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ were prepared using mixed binary chalcogenides powders. It was observed that Cu concentration was a function of substrate temperature as well as CuSe mole ratio in the target. Under an optimized condition, $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ thin films grew with strong [112]. [220/204] and [312/116] reflections. Both $Cu_2ZnSnSe_4\;and\;CulnZnSe_2$ films were found to exhibit a high absorption coefficient of $104^4cm^{-1}\;Cu_2ZnSnSe_4$ film showed a band gap of 1.5eV which closes to the optimum band gap of an ideal solar absorber for a solar cell. On the other side, an increase of optical band gap from 1.0 to 1.25eV was found to be proportional with an increase of Zn concentration in the $CulnZnSe_2$ film. All films in this study revealed a p-type semiconductor characteristic.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.105-111
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• 1999

When the preparation method of iron silicide films possess the annealing process, the interfacial state of the films is not fine. The good quality films were obtained as the plasma was used without annealing processing. Since the injected precursors were various active species in the plasma state, the organic compound was contained in the prepared films. We confirmed the formation of Fe-Si bonds as well as the organic compound by Fe and Si vibration mode in Raman scattering spectrum at $250cm^{-1}$ and Ft-IR. Because of epitaxy growth being progressed by the high energy of plasma at the low temperature of substrate, iron silicide was epitaxially grown to ${\beta}$-phase that had lattice structure such as [220]/[202] and [115]. Band gap of the prepared films had value of 1.182~1.174 eV and optical gap energy was shown value of 3.4~3.7 eV. The Urbach tail and the sub-band-gap absorptions were appeared by organic compound in films. We knew that the prepared films by plasma were obtained a good quality films because of being grown single crystal.

• Transactions on Electrical and Electronic Materials
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• v.2 no.1
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• pp.27-31
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• 2001

$\beta$-$In_2S_3$ and $\beta$-$In_2S_3$:$Co^{2+}$ thin films were grown using the spray pyrolysis method. The thin films crystallized into tetragonal structures. The indirect energy band gap of the thin films was found to be 2.32 eV for $\beta$-$In_2S_3$ and 1.81 eV for $\beta$-$In_2S_3$:$Co^{2+}$(Co:1.0 mol%) at 198K. The direct energy band gap was found to be 2.67 eV for $\beta$-$In_2S_3$ and 2.17 eV for $\beta$-$In_2S_3$:$Co^{2+}$(Co:1.0 mol%). Impurity optical absorption peaks were observed for the ${\beta}$-$In_2S_3$:$Co^{2+}$ thin films. These impurity absorption peaks are assigned, based on the crystal field theory, to the electron transitions between the energy levels of the $Co^{2+}$ ion sited in $T_{d}$ symmetry.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.128-132
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• 2013

L-Arginine semi-oxalate (LASO) single crystal has been grown by solution growth technique at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by single crystal X-ray diffraction studies. Photoluminescence studies confirm the violet fluorescence emission peak at 395 nm. Optical constants like band gap, refractive index, reflectance, extinction coefficient and electric susceptibility were determined from UV-VIS-NIR spectrum. The dielectric constant, dielectric loss and ac conductivity of the compound were calculated at different temperatures and frequencies to analyze the electrical properties. The solid state parameters such as plasma energy, Penn gap, Fermi energy and polarizability were calculated to analyze second harmonic generation (SHG). Nonlinear optical property was discussed to confirm the SHG efficiency of the grown crystal.