Modified Random-element Isodisplacement Model Research Articles

Raman scattering from vibrational and electronic excitations in a II-VI quaternary compound: Cd1-x-yZnxMnyTe.

The Raman scattering in a II-VI quaternary compound (${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Mn}}_{\mathit{y}}$Te) exhibits zone-center optical phonons whose frequencies vary with composition in a manner amenable to an extension of the modified random-element isodisplacement model. As a member of diluted magnetic semiconductors, ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Mn}}_{\mathit{y}}$Te exhibits the characteristic large magnetic-field-dependent redshift of the excitonic photoluminescence, the Raman-electron paramagnetic resonance of ${\mathrm{Mn}}^{2+}$, and an evidence of the Raman-antiferromagnetic resonance.

Long-wavelength lattice dynamics of GaxIn1−xAsySb1−y quaternary alloys

The quaternary semiconductor alloy GaxIn1−xAsySb1−y has been investigated using Raman scattering spectroscopy in the spectral region from 150 to 300 cm−1 at room temperature. The Raman spectra exhibit two- or three-mode behavior depending on the composition. A modified random-element isodisplacement model is used to describe the behavior of the optical phonons. The calculations of the dependence of the long-wavelength optical phonon frequencies on the composition are in good agreement with the experimental results.

A MREI Model for the Zincblende‐Like Phonons in the Mixed Defect Chalcopyrite ZnGa2(SxSe1–x)4

AbstractResults are given on the compositional dependence of the optical phonon frequencies in the pseudoternary defect chalcopyrite mixed crystals ZnGa2(SxSe1–x)4 over all the composition range. The compositional variation of the TO and LO highest frequency polar zincblende‐like phonons is explained in terms of a MREI (modified random element isodisplacement) model.

Raman and infrared studies of optical phonons in Zn1-xMnxTe mixed crystals

Raman and infrared reflectivity spectra of Zn1-xMnxTe mixed crystals were measured in the composition range 0<x<0.15. The experimental data obtained are analysed using the modified random-element isodisplacement model. It is found that the x dependence of the optical-phonon frequencies displays an intermediate behaviour between one- and two-mode type. A satisfactory agreement of the model with the experimental results is obtained only after the inclusion of force constants due to next-nearest neighbours.

A MREI Model for Zincblence‐Like Phonons in CdGa2(SxSe1−x)4 Mixed Crystals

AbstractResults are given of the Raman scattering measurements on the composition dependence of the optical phonon frequencies in the pseudoternary defect chalcopyrite mixed crystals CdGa2(SxSe1−x)4 over all the composition range. The mode behaviour of all Raman features is tracked and a MREI (modified random element isodisplacement) model to reproduce the concentration dependence of the highest frequency polar zincblende‐like modes is presented.

Lattice Vibrations of MgxCd1-xTe Mixed Crystals

Infrared and Raman measurements of lattice vibrations in Mg x Cd 1- x Te mixed crystals have been made in the concentration range x =0∼0.6. The modified random-element isodisplacement model has been applied to explain the concentration dependence of long wavelength longitudinal and transverse optic phonon frequencies in the mixed crystal system. From fitting the computed values to the experimental data we have estimated the static dielectric constant e 0 , TO and LO phonons of pure MgTe, and a gap made of Cd in MgTe.

Optical Phonons inGa1−xAlxAsMixed Crystals: A Modified Random-Element Isodisplacement-Model Calculation

The modified random-element isodisplacement model correctly predicts that ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ forms a two-mode-type mixed crystal. The model calculations agree very well with a recent infrared measurement of concentration dependence of long-wavelength longitudinal and transverse optic mode frequencies of the mixed-crystal system.

Application of a Modified Random-Element-Isodisplacement Model to Long-Wavelength Optic Phonons of Mixed Crystals

The random-element-isodisplacement (REI) model has been modified to include the polarization field, thereby enabling it to predict the long-wavelength longitudinal optic frequencies of a mixed crystal. A criterion has been obtained to determine whether a given mixed crystal will exhibit "one-mode" or "two-mode" behavior. Under certain conditions the modified REI (MREI) model may also be made to work for mixed crystals with one-mode behavior. The so-called "virtual-crystal model" applicable to this type of crystals becomes a special case of the MREI model. Given the properties of the "pure" end-members $\mathrm{AB}$ and $\mathrm{AC}$, the MREI model then can determine whether $A{B}_{1\ensuremath{-}x}{C}_{x}$ is going to display one-mode or two-mode behavior, and can predict the concentration dependence of the TO and LO modes. A large number of examples of both types of mixed crystals is given.