• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.3
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• pp.220-226
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• 2002

Amorphous $Sb_{2-x}Bi_xTe_3$ (x = 0.0, 0.5 and 1.0) thin films were prepared by vacuum evaporation. The resistivity of 7he films decreases from 1.4{\times}10^{-2}$ to $8.84{\times}10^{-5}\Omega cm$ and the type of conductivity changes from p to n with the increase of the x value of the films. D.C. conduction studies on these films ate performed at various electric fields in the temperature range of 303-403 K. At low electric fields, two types of conduction mechanisms, i.e. the variable range hopping and the phonon assisted hopping are found to be responsible for the conduction, depending upon the temperature. The activation energy decreases from 0.082 to 0.076 eV in the temperature range of 303-363 K and from 0.47-0.456 eV in the second range of 363-403 K, indicating the shift of the Fermi level towards the conduction band edge and hence the change of the conduction from P to n type with the increase of the Bi concentration. Poole-Frankel emission dominates at high fields. The shape of the potential well of the localized centre is deduced and the mean free path of the charge carriers is also calculated.

• Korean Journal of Materials Research
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• v.16 no.5
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• pp.292-296
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• 2006

Effects of rapid thermal annealing of bismuth telluride thin films on their thermoelectric properties were investigated. Films with four different compositions were elaborated by co-sputtering of Bi and Te targets. Rapid thermal treatments in range of $300{\sim}400^{\circ}C$ were carried out during 10 minutes under the reducing atmosphere (Ar with 10% $H_2$). As the temperature of thermal treatment increased, carrier concentrations of films decreased while their mobilities increased. These changes were clearly observed for the films close to the stoichiometric composition. Rapid thermal treatment was found to be effective in improving the thermoelectric properties of $Bi_2Te_3$ films. Recrystallization of $Bi_2Te_3$ phase has caused the enhancement of thermoelectric properties, along with the decrease of the carrier concentration. Maximum values of Seebeck coefficient and power factor were obtained for the films treated at $400^{\circ}C$ (about $-128{\mu}V/K$ and $9{\times}10^{-4}\;W/K^2m$, respectively). With further higher temperature ($500^{\circ}C$), thermoelectric properties deteriorated due to the evaporation of Te element and subsequent disruption of film's structure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.79-82
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• 2003

a-Se film is known as promising medical X-ray detector material but a-Se as dopanted Tellurium is not available in X-ray detectors. a-Se thick film was grown by vacuum thermal evaporator to $3{\mu}m$ thickness. The characteristics of thick films were analyzed by XRD, U-V Meter, and SEM measurements. Te composition is 0.1, 0.3, 0.5, 0.7g. This paper is fundmental data for phosphor layer's essential parameter that selenium have absorption wavelength along to various Te concentration rate.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.480-481
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• 2006

The n-type $(95%Bi_2Te_3-5%Bi_2Se_3)$ compound was newly fabricated by gas atomization and hot extrusion, which is considered to be a mass production technique of this alloy. The effect of powder size on thermoelectric properties of 0.04% $SbI_3$ doped $95%Bi_2Te_3-5%Bi_2Se_3$ alloy were investigated. Seebeck coefficient $({\alpha})$ and Electrical resistivity $(\rho)$ increased with increasing powder size due to the decrease in carrier concentration by oxygen content. With increasing powder size, the compressive strength of $95%Bi_2Te_3-5%Bi_2Se_3$ alloy was increased due to the relative high density. The compound with ${\sim}300\;{\mu}m$ size shows the highest power factor among the four different powder sizes. The rapidly solidified and hot extruded compound using $200[\sim}300{\mu}m$ powder size shows the highest compressive strength.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.138-139
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• 2006

Metal organic chemical vapor deposition has been investigated for growth of $Sb_{2-x}Bi_xTe_3$ films on (001) GaAs substrates using diisopropyltelluride, triethylantimony and trimethylbismuth as metal organic sources. The thermoelectric properties were measured at room temperature and include Seebeck coefficient, electrical conductivity and Hall effect. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's composition ratio and deposition temperature. The thermoelectric Power factor($={\alpha}^2{\sigma}$) was calculated from theses properties. The best Power factor was $2.6\;{\times}\;10^{-3}W/mK^2$, given by grown $Sb_{1.6}Bi_{0.4}Te_3$ at $450^{\circ}C$. These materials could potentially be incorporated into advanced thermoelectric unicouples for a variety of power generation applications.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.69-76
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• 1997

P-type ($Bi_{0.5}Sb_{1.5}Te_3$) and n-type ($Bi_2Te_{2.4} Se_{0.6}$) thermoelectric thin film were deposited on glass and Teflon substrates by the flash evaporation technique. The changes in thermoelectric properties, such as Seebeck coefficient, electrical conductivity, carrier concentration, carrier mobility, thermal conductivity, and figure of merit, were investigated as a function of film thickness and annealing condition. Figures of merit of the thin films annealed at 473 K for 1 hour were improved to be $1.3{\times}10^{-3}K^{-1}$ for p-type and $0.3{\times}10^{-3}K^{-1}$ for n-type, and they were almost independent of film thickness. Temperature sensors were fabricated from the thin films having the above mentioned properties. And thermo-emf, sensitivity, and time constant of the sensors were measured to evaluate their characteristics for temperature sensors. Thin film sensors deposited on Teflon substrates showed better performance than those on glass substrates, and their sensitivity and time constant were 2.91 V/W and 28.2 sec respectively for the sensor of leg width 1 mm$\times$length 16 mm.

• Journal of The Korean Society of Grassland and Forage Science
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• v.22 no.2
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• pp.131-136
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• 2002

A field experiment was carried out to compare the nitrate nitrogen concentration, sugar content and animal intake of low $sorghum{\times}sudangrass$ hybrids (Sorghum bicolor (L.) Moench) grown under application of animal manure in 1995. The application amount of animal manure were 40MT in cattle manure, and 30MT/ha in swine and poultry manure. The four NLCF's recommended hybrids used in this study were Pioneer 988, TE-Haygrazer and NC+ 855 (heading type), and Jumbo(headless type). The nitrate nitrogen concentration of forage was 365mg/kg at 50~60cm of plant height, 501mg at 100~120cm, and 502mg at 200~220cm, regardless of animal manure type and cultivar. The nitrate nitrogen concentration of NC+ 855 and P 988 was 519 and 526mg, respectively, and were higher than that(317mg) of Jumbo(P<0.05). The nitrate nioogen concentration of stems was 376mg, and significantly higher than that(135mg) of leaves(P<0.05) regardless of cultivar, and lower parts of stems and leaves were higher than those of upper parts of plants. The sugar contents of four $sorghum{\times}sudangrass$ hybrids were ranged between 3.1 and $3.7^{\circ}$ in cattle manure, 2.9 and $3.3^{\circ}$ in swine manure, and 2.8 and $4.9^{\circ}$ in poultry manure. The sugar content of NC+ 855 was the highest as $3.9^{\circ}$, p 988 was second as $3.4^{\circ}$, and then TE-Haygrazer and Jumbo were lower as $3.2^{\circ}$ and $2.9^{\circ}$, respectively. Animal intake of sorghum ${\times}$ sudangrass hybrids P 988 and NC+ 855 were slightly higher than those of Jumbo and TE-Haygrazer grown under application of cattle manure. Also the average intake of P 988 was a little higher than that of Jumbo. However, there were no significant differences of forage intake among few recommended $sorghum{\times}sudangrass$ hybrids.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.375-375
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• 2010

CdTe as an absorber material is widely used in thin film solar cells with the heterostructure due to its almost ideal band gap energy of 1.45 eV, high photovoltaic conversion efficiency, low cost and stable performance. The deposition methods and preparation conditions for the fabrication of CdTe are very important for the achievement of high solar cell conversion efficiency. There are some rearranged reports about the deposition methods available for the preparation of CdTe thin films such as close spaced sublimation (CSS), physical vapor deposition (PVD), vacuum evaporation, vapor transport deposition (VTD), closed space vapor transport, electrodeposition, screen printing, spray pyrolysis, metalorganic chemical vapor deposition (MOCVD), and RF sputtering. The RF sputtering method for the preparation of CdTe thin films has important advantages in that the thin films can be prepared at low growth temperatures with large-area deposition suitable for mass-production. The authors reported that the optical and electrical properties of CdTe thin film were closely connected by the thickness-uniformity of the film in the previous study [1], which means that the better optical absorbance and the higher carrier concentration could be obtained in the better condition of thickness-uniformity for CdTe thin film. The thickness-uniformity could be controlled and improved by the some process parameters such as vacuum level and RF power in the sputtering process of CdTe thin films. However, there is a limitation to improve the thickness-uniformity only in the preparation process [1]. So it is necessary to introduce the external or additional method for improving the thickness-uniformity of CdTe thin film because the cell size of thin film solar cell will be enlarged. Therefore, the authors firstly applied the chemical mechanical polishing (CMP) process to improving the thickness-uniformity of CdTe thin films with a G&P POLI-450 CMP polisher [2]. CMP process is the most important process in semiconductor manufacturing processes in order to planarize the surface of the wafer even over 300 mm and to form the copper interconnects with damascene process. Some important CMP characteristics for CdTe were obtained including removal rate (RR), WIWNU%, RMS roughness, and peak-to-valley roughness [2]. With these important results, the CMP process for CdTe thin films was performed to improve the thickness-uniformity of the sputtering-deposited CdTe thin film which had the worst two thickness-uniformities of them. Some optical properties including optical transmittance and absorbance of the CdTe thin films were measured by using a UV-Visible spectrophotometer (Varian Techtron, Cary500scan) in the range of 400 - 800 nm. After CMP process, the thickness-uniformities became better than that of the best condition in the previous sputtering process of CdTe thin films. Consequently, the optical properties were directly affected by the thickness-uniformity of CdTe thin film. The absorbance of CdTe thin films was improved although the thickness of CdTe thin film was not changed.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.117-124
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• 2015

In this paper, we introduce how to control TR, TE physical MR parameters for managing $H_1$ spin's SI(Signal Intensity) which is combined with gadolinium following administration MR agent in T1 effect for diagnostic usefulness. we used MRI phantom made with 0.5 mol Gadoteridol. This phantom was scanned by FSE sequence with different TR, TE parameters. In this study, to make T1 effect, TR was 200, 250, 300, 350, 400, 450, 500, 550, 600 msec. In addition to, TE was 6.2, 12.4, 18.6, 21.6 msec. The results were as follows ; Each RSP(Reaction Starting Point) was 100, 50, 40, 30 mmol in TE 6.2, 12.4, 18.6, 21.6 msec being irrelevant to TR. In MPSI(Max Peak Signal Intensity), 4 mmol was showed in TR 200 msec while peak signal was decreased to low concentration mol in TR 250-600 msec. In terms of RA(Reaction Area), the highest SI was TE 6.2 msec in TR 200-600msec. According to the study, we are able to recognize it is possible to control enhance rates by managing TR and TE of MR parameters; moreover, we expect that enhanced T1 image in MR clinical field can be performed in a practical way with this quantitative data.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.257-263
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• 2000

Thermoelectric properties of the 0.05wt% $SbI_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy, prepared by melting/grinding and hot pressing, were investigated with variation of the annealing time up to 36 hours. The electron concentration of the 0.05wt% SbI$_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy decreased with increasing the annealing time. The figure-of-merit of the 0.05wt% $SbI_3$-doped n-type $Bi_2(Te_{0.95}Se_{0.05})_3$ alloy was improved from $2.1{\times}10^{-3}/K$ to $2.35{\times}10^{-3}/K$ by annealing at $500^{\circ}C$ for 3 hours. When annealed longer than 12 hours, however, the figure-of-merit decreased substantially due to the increase of the electrical resistivity.