• Journal of the Korean Chemical Society
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• v.54 no.1
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• pp.120-124
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• 2010

$TiO_2$ and N-substituted $TiO_{2-x}N_x$ were synthesized by using precipitation method. $TiO_{2-x}N_x$ compound absorbed whole UV light as well as long wavelength of visible light (400 - 700 nm) because of the change of band gap from 3.2 eV to 1.77 eV. Results obtained revealed that $TiO_{2-x}N_x$ showed higher activity than pure $TiO_2$ or P-25 for visible-photocatalytic degradation of 1,4-dichlorobenzene.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.54-57
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• 2002

We have grown undoped $In_ xGa_{1-x}N,\; In_xGa_{1-x}N:Si\;and\;In_{0.1}Ga_{0.9}N:Zn$ thin films by MOCVD at temperature between 880 and $710^{\circ}C which endows various In composition in the epilayer from 0.07 to 0.22 as examined using X-ray diffraction, optical absorption(OA), photocurrent (PC) and photoluminescence (PL). The In molar fraction estimated from PL results is higher than that from the OA, PC, and X-ray data for $X{\le}0.22$, which may be caused by phase separation. However, the In molar fraction estimated by X-ray diffraction, OA, PC and PL for $In_xGa_{1-x}N:Si$ does not show discrepancy. With the appropriate Zn doping in undoped $In_{0.1}Ga_{0.9}N$, the emission peak is shifted from 3.15 eV which originates from the band edge emission peak to 2.65 eV which resulted from the conduction band to acceptor transition due to a deep acceptor level.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.225-231
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• 2016

The valence band maximum (VBM) and conduction band minimum (CBM) of Al-doped GaInAsSb alloys substrated on GaSb are calculated by using an analytic approximation based on the tight binding method. The relative positions of the VBM and CBM between Al-GaInASSb and GaSb determine band alignement type, valence band offset (VBO) and conductin band offset (CBO) for the heterojunctions. In this study, aluminium doping is assumed to be substituted in the cation site and limited up to 20 % because it can easily oxidize and degrade materials. It is found that the Al-doped alloys exhibit type-II band alignments over the entire composition range and make the band gaps increase, whereas the VBO and CBO decrease. The decreasing rate of VBO is higher than that of CBO, which implies the Al components play a decisive role in controlling electrons at the interface. The Al-dopled GaInAsSb alloy has a direct band gap induced by $E({\Gamma})$ with a considerable distance from the E(L) and E(X), however, $E({\Gamma})$ approaches to E(L) and E(X) in the high Sb concentration (Sb > 0.7-0.8) which might affect the electron mobility and degrade the optical quality.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.201-205
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• 2000

The colors of a tinted lens for a mixed color could be applied to a subtractive mixture's law, and the estimation of a tinted lens used the properties of optical absorptions and the color analysis. The optical absorption properties of Yellow(x)-Blue(1-x) depended on the yellow color in short wavelength below 500 nm, the absorption in the 550~650 nm wavelength regions depended on the blue color. The absorption band in the 550~650 nm wavelength regions was a peak for an ion of transition metal. The color properties of Yellow(x)-Blue(1-x) analysing by the $L^*a^*b^*$ of CIE system shifted to toward $+a^*$ decreasing x, it was formed of a pure color because of a low saturation existing in +0.6.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.267-273
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• 1998

The band structures of $Si_{1-x}Ge_x$ layers grown on $Si_{1-y}Ge_y$ substrate are calculated using k$\cdot$p and strain Hamiltonians. The hole drift mobilities in the plane direction are then calculated by taking into account the screening effect and the density-of-states of the impurity band. When $Si_{1-x}Ge_x$ is grown on Si substrate, the mobilities of (110) and (111) $Si_{1-x}Ge_x$ layers are larger than that of (001) $Si_{1-x}Ge_x$. However, due to the large defect and surface scattering, (110) and (111) $Si_{1-x}Ge_x$ layers may not be useful for the development of the fast device. Meanwhile, when Si is grown on $Si_{1-y}Ge_y$ substrate, the mobilities of (001) and (110) Si layers are greatly enhanced. Based on the amount of defect and the surface scattering, it is expected that Si grown on (001) $Si_{1-y}Ge_y$ substrate, where the Ge contents is larger than 10%(y>0.1), has the highest mobility.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.430-433
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• 2017

This paper presents a S/C/X-band LNA MMIC with resistive feedback structure in 0.25 um GaN HEMT process. The GaN devices have advantages as a high output power device having high breakdown voltage, energy band gap and stability at high temperature. Since the receiver using the GaN device with high linearity can be implemented without a limiter, the noise figure of the receiver can be improved and the size of receiver module can be reduced. The proposed GaN LNA MMIC based on 0.25 um GaN HEMT device is achieved the gain of > 15 dB, the noise figure of < 3 dB, the input return loss of > 13 dB, and the output return loss of > 8 dB in the S/C/X-band. The current consumption of GaN LNA MMIC is 70 mA with the drain voltage 20 V and the gate voltage -3 V.

• Bulletin of the Korean Chemical Society
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• v.27 no.3
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• pp.363-367
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• 2006

The structure-property relations of ternary copper chalcogenides, $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ are examined. The density of states, band dispersions, and Fermi surfaces of these compounds are investigated to verify the reason of the metal-insulator transitions by extended Huckel tight-binding band calculations. The origin of the metalinsulator transitions of non-stoichiometric $TlCu_{3-x}S_2$ and $\alpha-BaCu_{2-x}S_2$ is thought to be the electronic instability induced by their Fermi surface nesting.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.10
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• pp.42-48
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• 1992

RoA is an important figure of merits for estimating the performance of p-n junction infrared detectors. This paper presents the tunneling current contribution to RoA of $Hg_{1-x}Cd_{x}$Te n$^{+}$-p juction photodiodes. Then, a diffusion model, a thermal generation-recombination model, an indirect tunneling model via trap, and a band-to-band direct tunneling model are considered to calculate RoA. Using these models, RoA depending on temperature, doping concentration, and mole fraction is calculated. Also from these results, under various operating conditions the dominant dark current mechanisms cna be understood.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.3
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• pp.420-431
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• 1994

The HgCdTe material, which is II-VI compound semiconductor, is important materials for the fabrication of the infrared detectros. To suggest the model of accurate MIS C-V calculation for narrow band gap semiconductors such as HgCdTe, non-parabolicity from k.p theory and degeneracy effect are considered. And partially ionized effect and compensation effect which are material's properties are also considerd. Especially, degenerated material C-V characteristics from Fermi-Dirac statistics and exact charge theory are presented to get more accurate analysis of the experimental results. Also the comparison with calculation results between the general MIS theory from Boltzmann appoximation method and this model which is considered the narrow band gap semiconductor properties, show that this model is more useful theory to determination of accurate low and high frequency C-V characteristics.

• Bulletin of the Korean Chemical Society
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• v.20 no.9
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• pp.1045-1048
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• 1999

Electronic structures calculated based upon the extended Huckel tight-binding method for Ba1-xKxBiO3 with x = 0, 0.04, and 0.4 are reported. It is noticed that the commensurate ordering of Bi 3+ and Bi 5+ is responsible for the insulating and semiconducting behavior in BaBiO3 and Ba0.96K0.04BiO4. The band gaps of 3.2 eV and 1.4 eV for the former and the latter compounds, respectively, are consistent with the experimental results. Doping in Bi 6s-block band up to x = 0.4 causes the collapse of the ordering of Bi 3+ and Bi 5+, thereby resulting in the superconductivity in the Ba0.6K0.4BiO3 compound. Strikingly, the character of oxygen contributes to the conducting mechanism than that of the bismuth. This is quite different from the cuprate superconductors in which the character of copper dominates that of oxygen.