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Optical, Electrical, and Magneto-Optical Properties for Bulk Cd0.63-yMn0.37HgyTe Single Crystals
황영훈,Youngho Um,Hyekyeong Kim,Hyoyeol Park,Sunglae Cho 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
We investigated the magneto-optical properties of diluted magnetic semiconductor Cd$_{0.63-y}$ Mn$_{0.37}$Hg$_{y}$Te single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of $y$ $\leq$ 0.07. The band gap energy increases with increasing for $y$ $\leq$ 0.03, while decreasing with increasing for $y$ $\geq$ 0.03. An anomalous behavior was also observed in the magnetic susceptibility and the electrical resistivity. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant showed a maximum for the sample with $y$ = 0.03, and the value was approximately four times larger than that of the Cd$_{0.63}$Mn$_{0.37}$Te crystal. The Verdet constant had a maximum around Hg compositions with $y~\sim$ 0.03, and this result agrees well with the behavior of the magnetic susceptibility. This result reflects that Hg ion mediates and enhances the spin-spin interaction between Mn$^{2+}$ ions with increasing Hg composition up to $y~\sim$ 0.03.
Cd1-xMnTe(0.0 ≤x≤0.77) 단결정의 분광 타원해석법 연구
황영훈,엄영호,박효열 한국물리학회 2010 새물리 Vol.60 No.7
We used spectroscopic ellipsometry to investigate in the energy range of 1.5 - 5.5 eV at room temperature the dielectric function of Cd1-xMnxTe (0.0 ≤ x ≤ 0.77) crystals grown using a vertical Bridgman method. The critical point (CP) parameters of the E0, E1, and E1+Δ1 structure were determined from an analysis of the numerically-obtained second derivatives of the original pseudo-dielectric function spectra. The E1 and E1+Δ1 energies decreased with increasing Mn composition x due to a hybridization of the valence and the conduction bands in CdTe with Mn 3d levels. The dependence of such CP parameters on the Mn mole fraction x is discussed. 수직 Bridgman법으로 성장시킨 Cd1-xMnxTe (0.0≤x≤ 0.77)단결정의 복소 유전함수를 분광 타원해석기로 실온에서 1.5- 5.5 eV 에너지 범위에서 조사하였다. 유사 유전함수 스펙트럼의 2차미분을 SCP 모델로 분석하여 E0, E1, 및 E1+Δ1 구조의CP 매개변수를 결정하였다. E1 과 E1+Δ1 CP 에너지는조성비 증가에 대하여 감소함을 관측하였으며, 이는 Mn 3d 준위와CdTe의 가전자 및 전도 띠들과의 혼성(hybridaztion) 효과 때문이다. 조성비에 변화에 따른 CP 에너지와 Lorentzian broadening을 논의하였다.
Structural and magnetic properties of tetragonal Mn1.19Fe0.81As thin film grown on Si(001)
황영훈,조성래,최정용,이민규,한석희,Sungyoul Choi,김용함 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.-
We have successfully grown MnxFe2-xAs (x = 1.19) thin film on Si(001) substrate by molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) studies indicate the rough film surface and c-axis orientation in a tetragonal crystal structure. Mn1.19Fe0.81As film exhibited ferrimagnetic ordering at room temperature, which is supported by magnetization, magnetoresistance and anomalous-Hall-effect measurements.
Photoluminescence of Zn1-xBexSe Films Grown by Using Molecular Beam Epitaxy
황영훈,Youngho Um,Hyekyeong Kim,J.K Furdyna 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
We report a systematic investigation of band-edge photoluminescence of the II-VI wide band-gap semiconductor Zn$_{1-x}$Be$_{x}$Se for a series of Be compositions (0 $<$ $x$ $<$ 0.4). The specimens investigated were in the form of thin films fabricated by using molecular beam epitaxy (MBE). The near band-edge emissions of free excitons (designated as FX) were systematically investigated as a function of temperature and of alloy composition. From the temperature dependence of the free exciton peak, the Varshni temperature parameters $\alpha$ and $\beta$ were found to increase with increasing Be concentration $x$. From the temperature dependence of the FWHM of the free exciton FX emission line, the broadening factors $\Gamma (T)$ were determined from a fit to the data. Furthermore, the activation energies of thermal quenching for the E$_A$ peak were obtained from the temperature dependence of the free exciton peaks, and were found to decrease with increasing Be concentration.
Spectral Dependence of the Dielectric Function of Quaternary CdMnCoTe by Spectroscopic Ellipsometry
황영훈,Youngho Um,Hyekyeong Kim,Hyoyeol Park 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III
Spectroscopic ellipsometry measurements of the complex dielectric function of a series of Cd$_{0.63-y}$Mn$_{0.37}$Co$_y$Te single crystals grown by the vertical Bridgman method have been performed in the 1.5 $\sim$ 5.5 eV energy range at room temperature. The measurement data were analyzed by fitting the second-derivative spectra ($d^2 \varepsilon$/$d \omega^2$) with a theoretical model, namely, the standard critical-point (SCP) line shapes. The $E_1$, $E_1$+$\Delta_1$ and $E_2$ energies decreased with increasing Co composition $y$, which is due to the hybridization effect of the valence and conduction bands in Cd$_{1-x}$Mn$_x$Te with Co $3d$ levels.
황영훈,Youngho Um,Hyekyeong Kim,Sunglae Cho 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
We studied the dependence of the magnetic properties on the Mn concentration of IV-VI diluted magnetic semiconductor Si1.xMnxTe1.5 single crystals prepared by using the vertical Bridgman technique. X-ray studies showed that the crystal structure was hexagonal. The magnetization measurement of Si1.xMnxTe1.5 showed a ferromagnetic ordering up to 80 K. With increasing Mn concentration, the saturation magnetization increased and the coercive field increased, as shown in the hysteresis loop. For x = 0.20 and 0.31, a slope change in the resistivity was observed around 80 K and corresponded to a ferromagnetic (FM)-paramagnetic (PM) phase transition.
Temperature Dependence of the Band-Edge Photoluminescence of Mn-Doped ZnO Ceramics
황영훈,엄영호,조성래 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1
We investigated of the near band-edge photoluminescence of the diluted magnetic semiconductor alloy Mn-doped ZnO. The near band-edge emissions of the excitonic transition were systemati- cally investigated as a function of temperature. From the temperature dependence of the exciton peak, the Varshni temperature parameter, α, was found to increase with increasing Mn. From the temperature dependence of the FWHM of the emission line, the broadening factors, Γ(T), were determined from fits to the data. The activation energies of thermal quenching were obtained for both the D0X and the A0X peaks from the temperature dependence of the bound exciton peaks. Finally, we show that at high temperatures, the broadening of the FWHM is dominated by the LO phonon interaction.