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

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+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+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.ope

Structural, electrical, and ellipsometric properties of nitrogen-annealed ZnO:Al films

We have investigated the effects of nitrogen annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films deposited by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, films have highly crystalline structure with a c-axis preferred orientation. The most improvements in the electrical and optical properties of the ZnO:Al films were obtained by nitrogen annealing. The ZnO:Al films exhibited an average optical transmittance of 90–95% in the visible range and a sharp fundamental absorption edge. Spectroscopic ellipsometry (SE) was used to extract the optical constants of thin films. The optical characteristics of ZnO:Al films were modeled using a Tauc–Lorentz based dielectric function. The bandgap energy increased with the increases in nitrogen annealing temperature, which change in accordance with the Burstein–Moss effect, and was consistent with the observed changes in the transport properties.ope

Temperature Dependence of the Band-Edge Photoluminescence of Mn-Doped ZnO Ceramics

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 systematically investigated as a function of temperature. From the temperature dependence of the exciton peak, the Varshni temperature parameter, ??, was found to increase with increasing Mn. From the temperature dependence of the FWHM of the emission line, the broadening factors, (T), were determined from fits to the data. The activation energies of thermal quenching were obtained for both the D 0X and the A 0X 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.ope

Studies of Spectroscopic Ellipsometry in Cd1&#8722;xMnxTe (0.0< x< 0.77) Single Crystals

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+???1 structure were determined from an analysis of the numerically-obtained second derivatives of the original pseudodielectric function spectra. The E1 and E1+ ???1 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.ope

Weak ferromagnetism in CdMnZnTe single crystal

We studied the magnetic properties of diluted magnetic semiconductors Cd0.65&#8211;yMn0.35Zny Te single crystals grown using a vertical Bridgman method. The Cd0.65&#8211;yMn0.35Zny Te crystals with various Zn mole fractions have been grown in the zinc-blende structure. The band-gap energy obtained from the optical absorption spectrum at 300 K is linearly increased with increasing the addition of Zn into CdMnTe, which may be due to a decrease in the lattice constant. We have observed that the Cd0.22Mn0.35Zn0.43Te crystal showed weak ferromagnetic ordering up to 300 K, and the coercive field was 25 Oe at 250 K. The magnetic moment showed a maximum for the sample with y = 0.43, and the value was approximately ten times larger than that of the Cd0.65Mn0.35Te crystal. This result reflects that Zn ion mediates and enhances the spin-spin interaction between Mn2+ ions with increasing Zn composition up to y = 0.43.ope

Composition-dependent Magnetic Properties of Si1-xMnx (0.1 < x < 0.9) Single Crystals

In this study, we investigated the optical, magnetic, and electrical transport properties of Si1-xMnx(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 T-C = 30 K. The Si0.25Mn0.75 and Si0.18Mn0.82 alloys showed weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, as confirmed by magnetization, neutron diffraction, and transport studies.ope

Giant Faraday rotation in Cd1&#8211;xMnxTe (0 < x < 0.82) crystals

We investigated the magneto-optical properties of diluted magnetic semiconductors Cd1-xMnxTe crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of x < 0.82. The band-gap energy was depended on Mn mole fraction x linearly and increased with decreasing temperature. The increase of the energy gap with increasing x may be due to a decrease in the lattice constant. Faraday rotation as a function of photon energy with various Mn compositions for CdMnTe in the temperature range of 10-300 K has been measured. The Faraday rotation was increased as the photon energy increased near to that of the fundamental band gap. Verdet constant becomes larger since the effect of the sp-d exchange interaction is enhanced as the temperature is lowered.ope

Optical and electronic properties of highly stable and textured hydrogenated ZnO:Al thin films

We have experimentally investigated the effects of hydrogen-annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved optical transmission and enhanced absorption edge of the ZnO:Al film due to hydrogen-annealing. Our experimental data suggest the hydrogen-annealing process as an important role in the enhancement of electrical and optical properties, which is promising as a back reflector material for thin-film solar cells.ope

Magneto-optical properties for bulk Cd0.63&#8722;yMn0.37HgyTe single crystals

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxHgyTe (x similar to 0.37) single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of 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 10-300 K 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 10 K, 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 -0.87 deg/G cm at 613 nm, respectively. The Verdet constant showed a maximum for the sample with y=0.03, and the value is approximately four times larger than that of the Cd0.63Mn0.37Te crystal. The Verdet constant has a maximum around Hg compositions with y similar to 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 Mn2+ ions with increasing Hg composition up to y similar to 0.03.ope