• Korean Journal of Crystallography
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• v.14 no.2
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• pp.62-66
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• 2003

The preparation of n-type thermoelectric material of Bi₂ Te/sub 2.55/Se/sub 0.45/ doped with CuBr₂ was carried out using a vertical gradient freezing method. With this method, unidirectional solidified Bi₂Te/sub 2.55/Se/sub 0.45/ has been obtained. XRD analysis demonstrated that Bi₂/sub 2.55/Se/sub 0.45/ 5 ingot has grown with prefer orientation of (0 1 5) face. Seebeck coefficient and electrical conductivity were measured as functions of temperature in the range of 373 K to 523 K on the sample which prepared via VGF method.

• Proceedings of the Materials Research Society of Korea Conference
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• 2001.11a
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• pp.102-102
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• 2001

• Journal of Pharmacopuncture
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• v.21 no.1
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• pp.35-40
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• 2018

Objective: The role of BDNF (brain-derived neurotrophic factor), CREB (cAMP response element binding) and VGF neuropeptide has been proved in antidepressant activity of long term saffron administration in the rat hippocampus. In this study we evaluated the role of these proteins in antidepressant activity of saffron in long term administration in the rat cerebellum. Methods: Saffron aqueous extract (40 and 80 mg/kg/day) and imipramine (10 mg/kg/day) were administered intraperitoneally for 21 days to rats. At the end of experiment, animals were sacrificed and cerebellums were separated. The protein levels of BDNF, VGF, CREB and P- CREB in the rat cerebellum were evaluated using western blot analysis. Results: Saffron aqueous extract (80mg/kg/day) caused significant increase in protein level of P-CREB in long term treatment in the rat cerebellum. The increases in the protein levels of VGF, CREB and BDNF were not significant. Conclusion: In summary, our results showed that antidepressant effect of saffron in rat cerebellum might be due to the enhanced phosphorylation of CREB.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.1
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• pp.33-41
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• 1994

It is well known that the position and the shape of the S/L interface affect the qualities of the single crystal in the growth process. Thus the information of the temperature profile in the growth system is very important. In this study, we developed the program to predict the temperature profile from the setting values of the heating blocks in VGF(vertical gradient freezing) single crystal growth system. With this program, we studied the effects of the materials and the sizes of support rod, the materials of the crucible on the S/L interface shape. The larger radius and/or smaller thermal diffusivity support rod was, the flatter the S/L interface was. When the thermal conductivity of crucible was isotropic, the S/L interface was more concave downward to the solid phase in proportional to the increase of thermal diffusivity of the crucible. By the comparison of the S/L interface shape between PBN crucible and quartz crucible for the same condition, the effect of anisotropy of thermal conductivity of crucible showed different trends with respect to the position of the S/L interface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.1
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• pp.17-25
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• 1991

The construction details of VGF apparatus with a DM(direct monitoring) furnace for the growth of low defect crystal and characteristics of GaAs crystal grown by this apparatus are described. The average dislocation densities and EL2 concentration of as-grown undoped GaAs along the different solidified fractions exhibit $4{\times}10^{2}-7{\times}10^{3}cm^{-2}$ and $6{\times}10^{14}-4{\times}10^{15}cm^{-3}$, which are less than those observed for liquid encapsulated Czochralski(LEC) or high-pressure vertical gradient freeze(VGF) crystals. These remarkable reduction of the dislocation densities and EL2 concentrations were explained by the lower temperature gradient ($dT/dx-10^{\circ}/cm$) and slower rates of post - growth cooling ($20^{\circ}C/hr:1240-1000^{\circ}C,\;30^{\circ}C/hr:1000-700^{\circ}C$). Also, The Hall mobilities, carrier concentrations show uniform distribution throughtout 80% of the ingot length.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.2
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• pp.75-78
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• 2009

Si-doped GaAs single crystals were grown by vertical gradient freeze using PBN crucibles. The amount of oxide layer $B_{2}O_{3}$ in PBN crucible was changed($0{\sim}0.2wt%$) and measured the concentration of carriers. The segregation coefficients of Si in GaAs melt decreased rapidly from initial 0.1 to 0.01 as the amount of $B_{2}O_{3}$ increases. At the same time, concentration of carriers was shown to decrease. It is likely that the reaction between dopant Si and $B_{2}O_{3}$ in GaAs melt results in the reduction of Si dopants(donor) while increase in the amount of boron(acceptor). The thin layer of $B_{2}O_{3}$ glass in PBN crucible was proved to be a better way to reduce defect formation rather than the total amount of $B_{2}O_{3}$.

• Korean Journal of Crystallography
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• v.1 no.2
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• pp.115-125
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• 1990

We have investigated bulk and hetero-epitaxial growth of GaAs single crystal. Various growth techniques such as HB, HZM, and VGF for high quality bulk GaAs were successfully developed by appling the specially designed DM(direct monitoring) furnace. Al GaAs/GaAs superlattice structure and In(x)Ga(1-x) As/GaAs epilayers were also grown by MOCVD and VPE, respectively. The characterization of GaAs single crystals and epilayers was made by X-ray diffraction, Hall effect, PL, chemical etching and angle lapping technique.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.542-546
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• 1999

InP single crystal, III-V binary compound semiconductor, was grown by VGF(vertical gradient freeze) method using quartz ampoule and its electrical optical properties were investigated. Phosphorous powders were put in the bottom of quartz ampoule and Indium metal charged in conical quartz crucible what was attached at the upper side position inside the quartz ampoule. It was vacuous under the pressure of $10^5$Torr and sealed up. Indium metal was melted at $1070^{\circ}C$ and InP composition was formed by diffusion of phosphorous sublimated at $450^{\circ}C$ into Indium melt. By cooling the InP composition melt ($2^{\circ}C$~$5^{\circ}C$/hr of cooling rate) in range of $1070^{\circ}C$~$900^{\circ}C$, InP crystal was grown. The grown InP single crystals were investigated by X-ray analysis and polarized optical microscopy. Electrical properties were measured by Van der Pauw method. At the cooling method. At the cooling rate of $2^{\circ}C$/hr, growth direction of ingot was [111] and the quality of ingot was better at the upper side of ingot than the lower side. It was found that the InP crystals were n-type semiconductor and the carrier concentration, electron mobility and relative resistivity were $10^{15}$~$10^{16}/\textrm{cm}^3$ , $2\times 10^3$~$3\times 10^4{\textrm}{cm}^2$/Vsec and$2\times 10^{-1}$~$2\times 10^{-3}$/ Wcm in the range of 150K~300K, respectively.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.81-87
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• 1996

The mechanism of silicon incorporation has been analyzed for the boat-grown GaAs crystals on the basis of phase equilibrium in the Ga and As system. Comparison was made between silicon concentrations calculated from the thermodynamics of incorporation reaction and carrier concentrations measured from van der Pauw method. For the 1-T HB(single temperature zone horizontal Bridgman) crystals, calculated concentrations were 5.3 ×10 15 (atoms/cm3), measured as 9.8 ×10 15(/cm3) at the seed part. They were calculated to be 1.1 ×10 16(atoms/cm3) and measured as 1.5 ×10 16(/cm3) for the 2-T(double temperature zone) HB crystals. On the other hand, it was found to be closer between the calculated and measured silicon concentrations for the VGF(vertical gradient freeze) crystals, which were grown within half the run time compared with 1-T or 2-T HB method.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.419-431
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• 1999

InP, III-V binary compound semiconductor, single crystal was grown by VGF (vertical gradient freeze) method using quartz ampoule and its electrical optical properties were investigated. Phosphorous powders were put in the bottom of quartz ampoule and Indium metal changed in conical quartz crucible hat was attached at the upper side position inside the quartz ampoule. It was vacuous under the pressure of 10-5 Torr and sealed up. In metal in the quartz crucible was melted at 1070$^{\circ}C$ and phophorous sublimated at 450$^{\circ}C$, there after it was diffused in In melt and so InP composition was formed. By cooling the InP composition melt (2$^{\circ}C$∼5$^{\circ}C$/hr of cooling rate) in range of 1070$^{\circ}C$∼900$^{\circ}C$, InP crystal was grown. the grown InP single crystals were investigated by X-ray analysis and polarized optical microscopy. Electrical properties of them were measured by Van der Pauw method. At the cooling rate of 2$^{\circ}C$/hr, its direction was (111), quality of the ingot ws better upper side of the ingot than lower. It was found that the InP crystals were n-type semiconductor and the carrier concentration, electron mobility and relative resistivity were 1015∼1016/㎤, 2x103∼3x104$\textrm{cm}^2$/Vsec and 2x10-1∼2x10-3Ωcm in the range of 150K∼300K, respectively.