Hyoyeol Park

Temperature dependence of Vickers hardness for Cd1−xMnxTe (0⩽x⩽0.82) single crystals

The Cd1−xMnxTe (0⩽x⩽0.82) single crystals were grown by the vertical Bridgman method. The Vickers hardnesses of the grown crystals were measured as a function of Mn composition and temperature for the first time. The activation energy was determined for the dislocation motion from the relation between temperature and hardness, and it was decreased as increasing x in Cd1−xMnxTe single crystals. Also, the Vickers hardness HV was decreased as increasing temperature and increased as Mn composition x.

Magneto-optical properties for bulk Cd0.63−yMn0.37HgyTe single crystals

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd1−x−yMnxHgyTe (x∼0.37) single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of y⩽0.07. The band gap energy increases with increasing y (⩽0.03), while decreases with increasing y (⩾0.03). An anomalous behavior was also observed in the magnetic susceptibility and electrical resistivity. Faraday rotation as a function of photon energy with various Hg compositions for CdMnHgTe in the temperature range of 10–300K has been measured. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant becomes larger since the effect of the sp-d exchange interaction is enhanced as the temperature is lowered. At 10K, the Verdet constants of the Faraday rotation for the samples with y=0, 0.01, 0.03, 0.05, and 0.07 were observed to be −1.09, −2.57, −3.94, −0.97, and −0.87deg∕Gcm at 613nm, respectively. The Verdet constant showed a max...

Temperature dependence of the fundamental band gap energy of Cd1−xCoxTe single crystals

Abstract Cd1−xCoxTe single crystals were grown by the vertical Bridgman method. The optical band gap energy of Cd1−xCoxTe(x=0, 0.001, 0.004, 0.008) were obtained as a function of temperature (12 ∼ 300K) and cobalt composition x. The temperature variation of the energy gap could be well fitted by the empirical Varshni relation. The temperature coefficient at low temperature decreased with x, but was nearly constant at high temperature. The band gap energy decreased linearly with composition.

Photoluminescence characteristics of Cd1-xMnxTe single crystals grown by the vertical Bridgman method

In this paper, we report a systematic investigation of band-edge photoluminescence for Cd1-xMnxTe crystals grown by the vertical Bridgman method. The near-band-edge emissions of neutral acceptor-bound excitons (labeled as L1) were systematically investigated as a function of temperature and of alloy composition. The parameters that describe the temperature variation of the energy were evaluated by the semiempirical Varshni relation. From the temperature dependence of the full width at half maximum of the L1 emission line, the broadening factors Γ(T) were determined from the fit to the data. The activation energies of thermal quenching were obtained for the L1 peak from the temperature dependence of the bound exciton peaks and were found to decrease with increasing Mn concentration.

Spectroscopic Ellipsometry Studies of Cd1-xMnxTe Films Grown on GaAs

Spectroscopic ellipsometry measurements of the complex dielectric function of a series of Cd1-xMnxTe (0 ?x ?0.7) films grown on (100) GaAs by hot wall epitaxy have been performed in the 1.5?5.5 eV photon energy range at room temperature. The measured data were analyzed by fitting the second-derivative spectra (d2?/d?2) with a theoretical model, namely, the standard critical-point (SCP) line shapes. It was found that the SCP model explains the measured derivative spectra successfully. The composition dependence of the critical-point (CP) energies and Lorentzian broadening (?) was determined.

Composition-dependent Magnetic Properties of Si 1-x Mn x (0.1 < x <0.9) Single Crystals

In this study, we investigated the optical, magnetic, and electrical transport properties of Si 1-x Mn x (0.1 ＜ x ＜ 0.9) single crystals grown by the vertical Bridgman method. The alloys with a Mn concentration of up to 64% demonstrated weak ferromagnetic ordering around TC = 30 K. The Si 0.25 Mn 0.75 and Si 0.18 Mn 0.82 alloys showed weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, as confirmed by magnetization, neutron diffraction, and transport studies.

EXAFS Analysis of the Local Structure of Cd(1−x)MxTe (M=Cr, Fe, Ni)

CdTe, doped with transition metals, has received much attention for decades as promising II‐VI dilute magnetic semiconductor materials. High purity Cd(1−x)MxTe (M=Cr, Fe, Ni) monocrystals have been prepared by the Bridgman method. Because the solubility of transition metals in CdTe is rather small, the zinc‐blende phases were prepared in the limit of x ⩽ 0.1. The local structural relaxation and effects of metal ion substitution on CdTe have been studied by measuring the fluorescence detected X‐ray absorption fine structure (XAFS) spectra of the M K‐edges and Te L1‐edges. While II‐VI compounds show significant variations of band structures, carrier densities and mobilities depending on the amount of donor or acceptor, XANES and EXAFS analysis of the M K‐edge spectra reveal that only slight variations of oxidation states and bond lengths appear in no connection with atomic number of substituting metals, On the other hand, Te L1‐edge spectra, for example of Cd(1−x)FexTe, exhibit rather a strong distortion ar...

Excitation‐Power Dependence of the Near Band‐Edge PL Spectra of CdMnTe with High Mn Concentrations

Temperature and excitation power dependences of photoluminescence (PL) measurements were studied for the CdMnTe crystal grown by the vertical Bridgman method. The near band‐edge and intra‐Mn2+ emissions were investigated as a function of temperature. The observed band‐edge peak of the PL spectrum showed a clear blue‐shift with decreasing temperature. However, the peak energy of the intra‐Mn2+ transition did not decrease monotonically with changing temperature, as can be seen above 70 K. With increasing the excitation power, the intensity of the emission peak was increased.Temperature and excitation power dependences of photoluminescence (PL) measurements were studied for the CdMnTe crystal grown by the vertical Bridgman method. The near band‐edge and intra‐Mn2+ emissions were investigated as a function of temperature. The observed band‐edge peak of the PL spectrum showed a clear blue‐shift with decreasing temperature. However, the peak energy of the intra‐Mn2+ transition did not decrease monotonically with changing temperature, as can be seen above 70 K. With increasing the excitation power, the intensity of the emission peak was increased.