Chang-Sun Yoon

PHOTOLUMINESCENCE PROPERTIES OF MGXZN1-XSE SINGLE CRYSTALS

MgxZn1−xSe single crystals were grown by the closed tube sublimation method. The MgxZn1−xSe single crystals crystallized into zincblende and wurtzite structures in the composition ranges of x=0.0–0.1 and x=0.2–0.6, respectively. Blue and violet emissions with LO phonon replica and self-activated emissions in the MgxZn1−xSe single crystals were observed at 10 K.

Optical properties of ZnAl2Se4, ZnAl2Se4:Co2+, and ZnAl2Se4:Er3+ single crystals

Single crystals of ZnAl2Se4, ZnAl2Se4:Co2+, and ZnAl2Se4:Er3+ were grown by the chemical transport reaction method using iodine as a transporting material. It has been shown that these single crystals have a defect chalcopyrite structure and a direct band gap. The direct band gap at 13 K has been found to be 3.525 eV for ZnAl2Se4, 2.952 eV for ZnAl2Se4:Co2+, and 3.283 eV for ZnAl2Se4:Er3+, respectively. Impurity optical absorption spectra of ZnAl2Se4:Co2+ showed absorption characteristics of Co2+ ions due to electron transitions between their split energy levels under a Td symmetry crystal field. Photoluminescence spectra at 13 K of ZnAl2Se4 showed two emission bands centered at 470 and 799 nm. For ZnAl2Se4:Er3+, we observed sharp photoluminescence peaks due to emission transitions between the energy levels of Er3+ ions with S4 symmetry sites.

Growth and characterization of MgxCd1 − xSe single crystals

Single crystals of MgxCd1 − xSe over the range 0 ⩽ x ⩽ 0.46 were grown by the modified chemical transport reaction technique. The structural and optical properties of the MgxCd1 − xSe single crystals were investigated at room temperature from X-ray powder diffraction and optical absorption measurements. It has been found that the MgxCd1 − xSe has a wurtzite structure over the investigated composition range. The lattice constants of a and c decrease linearly with increasing a composition x. The band gap increases linearly with increasing a composition x, which is represented by a linear relationship Eg(x) = 1.742 + 1.813 x.

Disorder-induced Raman scattering in MgxZn1−xTe mixed crystals

Abstract The phonon spectra of the mixed crystal Mg x Zn 1− x Te (0 ≤ X ≤ 0.48) in the zinc-blende phase are investigated by Raman scattering. The phonon frequencies exhibit a dependence on the Mg concentration. The disorder induced one-phonon and two-phonon modes are present in the Raman spectra for X ≥ 0.16. The Raman intensity ratio between first-order and second-order phonon modes was a good indicator to characterize the degree of disorder in the mixed crystals.

Optical properties of CuAlSe2:Er3+ single crystal

Abstract CuAlSe 2 :Er 3+ single crystals were grown by the chemical transport reaction method. The single crystal crystallized in the chalcopyrite structure. The optical energy gap at 10 K was found to be 2.65 eV. The sharp impurity optical absorption peaks due to Er 3+ ion were observed at 544 nm, 657 nm, 980 nm, 990 nm, 1006 nm, 1014 nm and 1544 nm. The sharp photoluminescence peaks due to Er 3+ ion were observed at 544 nm, 654 nm, 661 nm and 667 nm, and the broad photoluminescence peak due to a donor-acceptor pair recombination was observed at 674 nm.

Optical properties of undoped and co-doped CuGa1−XAlXSe2 single crystals

Abstract Single crystals of CuGa 1− X Al X Se 2 and CuGa 1− X Al X Se 2 :Co 2+ were grown by the chemical transport reaction (CTR) method using iodine as the transport agent. From optical absorption spectra of these compounds, the composition dependence of the optical energy gap and the origin of the impurity optical absorption due to the cobalt impurity are investigated. The origin of the impurity optical absorption in CuGa − X Al X Se 2 :Co 2+ single crystals has been analyzed by the static crystal field theory. Co 2+ ions in CuGa 1− X Al X Se 2 :Co 2+ single crystals are located at the host lattice of CuGa 1− X Al X Se 2 single crystals with cubic T d symmetry. It was observed that the impurity absorption peaks are attributed to the electronic transitions between the split energy levels of Co 2+ ions.

Optical properties of undoped, Co2+- and Er3+-doped CdAl2Se4 single crystals

Abstract Single crystals of CdAl 2 Se 4 , CdAl 2 Se 4 :Co 2+ and CdAl 2 Se 4 :Er 3+ were grown by the chemical transport reaction method using iodine as a transporting material. The crystal structure of these single crystals has been shown to be a defect chalcopyrite, and the direct bandgap at 10 K has been found to be 3.082 eV for CdAl 2 Se 4 , 2.683 eV for CdAl 2 Se 4 :Co 2+ and 2.980 eV for CdAl 2 Se 4 :Er 3+ , respectively. We observed impurity optical absorption peaks due to electron transitions between the energy levels of Co 2+ ions sited at T d symmetry of the host material. We also observed two broad blue-green photoluminescence peaks centered at 458 and 539 nm in the photoluminescence spectrum at 10 K of CdAl 2 Se 4 single crystals. For CdAl 2 Se 4 :Er 3+ single crystals, on the other hand, sharp photoluminescence peaks were observed, which are due to emission transitions between the energy levels of Er 3+ ions with T d symmetry sites.

Structural and optical properties of and single crystals

and single crystals were grown by the closed tube sublimation method. The crystal structures and the composition dependence of the energy gaps of the single crystals were identified, and the impurity optical absorption in the single crystals were investigated. The origin of the impurity optical absorption was identified with electron transitions between the energy levels of the ion sited at the symmetry point.

Photoluminescence spectra of ZnAl2Se4-4xS4x single crystals

Single crystals of ZnAl2Se4-4xS4x quaternary solid solution were grown by the chemical transport reaction method. The ZnAl2Se4-4xS4x single crystals were found to have a defect chalcopyrite structure in the region of 0.0≤x≤0.2 and a cubic spinel in the region of 0.8≤x≤1.0. It was also shown in these regions that the lattice constants and optical energy gaps depend on a composition x. A miscibility region existed in the region of 0.2<x<0.8. The photoluminescence spectra for the crystals with 0.0≤x≤0.2 and 0.8≤x≤1.0 showed a strong blue emission band and a weak broad emission band due to donor-acceptor pair recombination at low temperatures. A simple energy band scheme for the radiative mechanism in the ZnAl2Se4-4xS4x was proposed on the basis of our experimental results along with the measurements of thermoluminescence and photo-induced current transient spectroscopy.

PHOTOLUMINESCENCE PROPERTIES OF MGXCD1 -XSE MIXED SINGLE CRYSTALS

The photoluminescence spectra of MgxCd1−xSe (0.00⩽x⩽0.46) mixed single crystals grown by the chemical transport reaction technique were investigated. We observed an emission band (I2) due to excitons bound to a neutral donor, an emission band (DA) due to donor-acceptor pair recombination with LO-phonon replicas and a self-activated emission band. These emission bands were shifted to higher energy with increasing x. For the crystals with x=0.46, the donor-acceptor emission band was observed at 2.661 eV in the blue region.