• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.273-280
• /
• 2002

The stochiometric mix of evaporating materials for the CuGaTe$_2$ single crystal thin films was prepared from horizontal furnance. For extrapolation method of X-ray diffraction patterns for the CuGaTe$_2$ polycrystal, it was found tetragonal structure whose lattice constant a$\_$0/ and c$\_$0/ were 6.025 ${\AA}$ and 11.931 ${\AA}$, respectively. To obtain the single crystal thin films, CuGaTe$_2$ mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were 670 $^{\circ}C$ and 410 $^{\circ}C$ respective1y, and the thickness of the single crystal thin films is 2.1 $\mu\textrm{m}$. The crystalline structure of single crystalthin films was investigated by the photoluminescence and 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 dependence on temperature. The carrier density and mobility of CuGaTe$_2$ single crystal thin films deduced from Hall data are 8.72${\times}$10$\^$23/㎥, 3.42${\times}$10$\^$-2/㎡/V$.$s at 293K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the CuGaTe$_2$ single crystal thin film, we have found that the values of spin orbit coupling Δs.o and the crystal field splitting Δcr were 0.0791 eV and 0/2463eV at 10K, respectively. From the PL spectra at 10K, 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 0.0470eV and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be 0.0490eV, 0.00558eV, respectively.

• Nuclear Engineering and Technology
• /
• v.51 no.3
• /
• pp.731-737
• /
• 2019

In this study, a new measurement method based on voltage transients in CdZnTe detectors response to low energy photon irradiations is applied to measure the electron mobility (${\mu}_e$) and electron mobility-lifetime product $({\mu}{\tau})_e$ in a CdZnTe detector. In the proposed method, the pulse rise times are derived from low energy photon response to 59.5 keV($^{241}Am$), 88 keV($^{109}Cd$) and 122 keV($^{57}Co$) ${\gamma}-rays$ for the irradiation of the cathode surface at each detector for different bias voltages. The electron $({\mu}{\tau})_e$ product was then determined by measuring the variation in the photopeak amplitude as a function of bias voltage at a given photon energy using a pulse-height analyzer. The $({\mu}{\tau})_e$ values were found to be $(9.6{\pm}1.4){\times}10^{-3}cm^2V^{-1}$ for $1000mm^3$, $(8.4{\pm}1.6){\times}10^{-3}cm^2V^{-1}$ for $1687.5mm^3$ and $(7.6{\pm}1.1){\times}10^{-3}cm^2V^{-1}$ for $2250mm^3$ CdZnTe detectors. Those results were then compared with the literature $({\mu}{\tau})_e$ values for CdZnTe detectors. The present results indicate that, the electron mobility ${\mu}_e$ and electron $({\mu}{\tau})_e$ values in CdZnTe detectors can be measured easily by applying voltage transients response to low energy photons, utilizing a fast signal acquisition and data reduction and evaluation.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.15 no.2
• /
• pp.243-248
• /
• 2015

We prepared semi-insulating CdTe for radiation detectors by isothermal annealing of single crystals grown by Bridgeman technique in a sealed quartz container filled with Sn vapor. The resistivity of CdTe:Sn samples thus obtained was of order of $10^{10}Ohm{\cdot}cm$ at room temperature with electrons lifetime of $2{\times}10^{-8}$ s, which is appropriate for the applications desired. Analysis of electric transport characteristics depending on temperature, sample thickness and voltage applied revealed the presence of traps with concentration of about $(4-5){\times}10^{12}cm^{-3}$ with the corresponding energy level at 0.8 - 0.9 eV counted from the bottom of conduction band. The conductivity was determined by electron injection from electrodes in space charge limited current mode.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.3
• /
• pp.127-131
• /
• 2003

High quality zincblende ZnTe(100) epilayers have been grown on semi-insulating $CaAs(100\pm2^{\circ})$substrate by hot-wall epitaxy. To grow high quality ZnTe epilayers, the growth temperature dependence of the surface topography, the growth rate, and the crystalline properties were investigated. From the photoluminescence measured at 10 K, the light hole and heavy hole free exciton emissions splitted by thermal tensile strain were observed and their first excited state emissions were also measured. The low temperature doublet of the heavy hole free exciton is because of the energy separation between longitudinal exciton and transverse exciton due to exciton-polariton coupling.

• Journal of Powder Materials
• /
• v.17 no.2
• /
• pp.107-112
• /
• 2010

Carbon-nanotube-embedded bismuth telluride (CNT/$Bi_2Te_3$) matrix composites were fabricated by a powder metallurgy process. Composite powders, whereby 5 vol.% of functionalized CNTs were homogeneously mixed with $Bi_2Te_3$ alloying powders, were successfully synthesized by using high-energy ball milling process. The powders were consolidated into bulk CNT/$Bi_2Te_3$ composites by spark plasma sintering process at $350^{\circ}C$ for 10 min. The fabricated composites showed the uniform mixing and homogeneous dispersion of CNTs in the $Bi_2Te_3$ matrix. Seebeck coefficient of CNT/$Bi_2Te_3$ composites reveals that the composite has n-type semiconducting characteristics with values ranging $-55\;{\mu}V/K$ to $-95\;{\mu}V/K$ with increasing temperature. Furthermore, the significant reduction in thermal conductivity has been clearly observed in the composites. The results showed that CNT addition to thermoelectric materials could be useful method to obtain high thermoelectric performance.

• Journal of Ceramic Processing Research
• /
• v.20 no.6
• /
• pp.582-588
• /
• 2019

FeVSb1-xTex (0.02 ≤ x ≤ 0.10) half-Heusler alloys were fabricated by mechanical alloying process and subsequent vacuum hot pressing. Near single half-Heusler phases are formed in vacuum hot pressed samples but a second phase of FeSb2 couldn't be avoided. After doping, the lattice thermal conductivity in the system was shown to decrease with increasing Te concentration and with increasing temperature. The lowest thermal conductivity was achieved for FeVSb0.94Te0.06 sample at about 657 K. This considerable reduction of thermal conductivities is attributed to the increased phonon scattering enhanced by defect structure, which is formed by doping of Te at Sb site. The phonon scattering might also increase at grain boundaries due to the formation of fine grain structure. The Seebeck coefficient increased considerably as well, consequently optimizing the thermoelectric figure of merit to a peak value of ~0.24 for FeVSb0.94Te0.06. Thermoelectric properties of various Te concentrations were investigated in the temperature range of around 300~973 K.

• The Journal of the Acoustical Society of Korea
• /
• v.34 no.4
• /
• pp.310-315
• /
• 2015

A single channel VAD (Voice Activity Detection) algorithm for nonstationary noise environment is proposed in this paper. Threshold values of the feature parameter for VAD decision are updated adaptively based on estimates of means and standard deviations of past non-speech frames. The feature parameter, SPD-TE (Spectral Power Difference-Teager Energy), is obtained by applying the Teager energy to the WPD (Wavelet Packet Decomposition) coefficients. It was reported previously that the SPD-TE is robust to noise as a feature for VAD. Experimental results by using TIMIT speech and NOISEX-92 noise databases show that decision accuracy of the proposed algorithm is comparable to several typical VAD algorithms including standards for SNR values ranging from 10 to -10 dB.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.2
• /
• pp.180-184
• /
• 1999

The single crystals of $Mg_{0.15}Zn_{0.85}Te$ and $Mg_{0.15}Zn_{0.85}Te:Co^{2+}$(0.001%) were grown by vertical Bridgman method. Optical absorption properties of this compound were studied. As a result of the optical absorption spectra of $Mg_{0.15}Zn_{0.85}Te$, absorption peaks were related to exciton and the exciton level redshifts with increasing temperature, and temperature coefficient given to the value of $-5.8{\times}10^{-4}\;eV/K$ for the temperature range above 100 K. in the $Mg_{0.15}Zn_{0.85}Te:Co^{2+}$(0.001%) single crystal, the intracenter transitions due to $Co^{2+}$ ions were detected for $A-band:^4A_2(^4F) {\to}^4T_1(^4F),\; B-band:\; ^4A_2(^4F){\to}^4T_1(^4P)$, and the charge transfer transition near the absorption edge was observed in the wavelength range of 500 to 800 nm. According to the crystal field theory and Lucovsky formula, the crystal field parameter, Racah parameter and charge transfer energy were determined.

• Journal of Powder Materials
• /
• v.12 no.6 s.53
• /
• pp.387-392
• /
• 2005

The p-type semiconductor $Bi_2Te_3-Sb_2Te_3$ thermoelectric materials were fabricated by melting, milling and sintering process and their thermoelectric properties were characterized. The compound materials were ball-milled with milling time and the powders were sintered by spark plasma sintering process. The ball milled powders had equiaxial shape and approedmately $1\~3{\mu}m$ in size. The figure of meritz of sintered thermoelectric materials decreased with milling time because of lowered electrical resistivity. The thermoelectric properties of $Bi_2Te_3-Sb_2Te_3$ materials have been discussed in terms of electrical property with ball mill process.

• Journal of Korea Foundry Society
• /
• v.10 no.4
• /
• pp.324-331
• /
• 1990

The single crystal of CdTe was grown by modified 6 zone Bridgman method under the conditions of excess Te and excess Cd. To prevent the constitutional supercooling, the crystal growth was done under the temperature gradient of $17^{\circ}C/cm$ in front of the solid /liquid interface and the growth rate was 3mm/hr. The grain morphologies and the growth mechanism were investigated in excess Te and excess Cd conditions. The grain size of excess Te crystal was increased with an increase of the distance from the tip but, in the case of excess Cd crystal, single crystal was not obtained because of the cavities due to the excess Cd vapors so that the grain size was not increased with an increase of the distance from the tip. In addition, the growth of single crystal of CdTe was done with repeated necking ampoule. It was found that the necking had no effects on the grain selection because the cavities trapped in the necking portion acted as heterogeneous nucleation sites.