Zinc-blende Alloys Research Articles

First-principles calculations to investigate electronic structure and optical spectra of CdxZn1-xS ternary semiconductor alloys

The structural parameters, electronic band structure and optical spectra of CdxZn1-xS (0 ≤ x ≤ 1) ternary semiconductor alloys are studied. The calculations are realized using the full potential linearized augmented plane wave method. The modified local density approximation (LDA) and generalized gradient approximation (GGA) have been used for describing the exchange-correlation potential. The obtained results for zinc-blende CdxZn1-xS ternary alloys show a general wellness with the data shown in the literature. An inspection of electronic band structure indicates that zinc-blende CdxZn1-xS are (Г→Г) direct band gap semiconductors (from x = 0 up to x = 1). A predominant ionic type of the chemical bonding in these materials has been indicated. The density of states shows various peaks in both valence and conduction localities proposing that an abundance of conditions is obtainable for occupation. The alloys affect the optical features of interest. The results obtained from the present work show that the zinc-blende CdxZn1-xS is a promettant material for photovoltaic device applications. Moreover, the alloy of interest can be used in different devices from visible to ultraviolet light.

Influence of pressure and composition on electronic properties, phonon frequencies, and sound velocity for the zinc-blende GaAs1-xNx alloy

We investigated the electronic, phonon frequencies, and sound velocity of GaAs1-xNx ternary semiconductor alloys with the zinc-blende crystal structure over the entire nitrogen concentration range (with x from 0 to 1) using the empirical pseudo-potential model within the virtual crystal approximation including the compositional disorder effect. The pressure-dependent electronic, phonon frequencies and sound velocity of GaAs1-xNx ternary alloy have been studied. Our findings and the existing experimental data are found to be in good agreement. According to the dependence on pressure, a rising bandgap is predicted for GaAs1-xNx alloys at high-pressure values. According to the findings of this study, the GaAs1-xNx characteristics could have substantial optoelectronic applications in the infrared and mid-infrared spectral ranges.

Materials properties, lattice dynamics and polaron characteristics in InSbxP1-x ternary alloys

The structural, elastic and piezoelectric properties of zinc-blende InSbxP1-x ternary alloys are presented. Besides, phonon modes and polaron characteristics are reported. In addition, many thermodynamic quantities in instance, thermal expansion coefficient, heat capacity and entropy are examined and discussed. A reasonably good accord is obtained between our calculated results and those quoted in the literature. The results regarding piezoelectric, thermal and polaron properties dependence on Sb concentration in InSbxP1-x may be seen as the first predictions.

First principle investigations of structural, electronic and magnetic properties of Cr doped zinc-blende MgTe ternary alloys with DFT based FP-LAPW approach

First principle calculations of structural, electronic and magnetic properties of transition metal Cr doped MgTe ternary alloys have been performed using density functional FP-LAPW methodology. The exchange–correlation potentials for ground state structural properties of CrxMg1-xTe (x = 0.0, 0.25, 0.50, 0.75, 1.0) alloys have been calculated with Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for electronic and magnetic properties with modified Becke-Johnson (mBJ)-GGA scheme. Calculations suggested that the CrxMg1-xTe compounds possess ferromagnetic zinc-blende structures. The analyses of density of states (DOS) show that spin polarisation of electron in Cr-d orbitals are responsible for the half-metallic ferromagnetic characters. In the study of magnetic properties, total magnetic moments of ternary alloys and their constituent atoms have been calculated and found that the major contribution comes from the Cr atom in each ternary alloy. The spin-exchange constant N0α and N0β have been calculated in order to validate the effects of exchange splitting in the specimens. Present calculations indicate that the ternary alloys are potential magnetic materials for various half-metallic ferromagnetic and spintronic applications.

Atomic distributions observed in group IV-IV binary tetrahedron alloys: A revised analysis of SiGe and GeSn compounds

This manuscript is an attempt to extend the Strained Tetrahedron Model to the interpretation of the EXAFS spectra of Group-IV-IV binary tetrahedron ordered B3 zinc blende alloys. The analysis clearly points out the difference of these systems respect to other binary alloys. To illustrate and describe the application of the Strained Tetrahedron Model a revised characterization of Ge1-xSix and Ge1-xSnx alloys is presented and discussed.

Bond-stretching force constants and vibrational frequencies in ternary zinc-blende alloys: A systematic comparison of (In,Ga)P, (In,Ga)As and Zn(Se,Te)

We present element-specific effective bond-stretching force constants and Einstein frequencies of (In,Ga)P ternary alloys determined by temperature-dependent extended x-ray absorption fine structure spectroscopy. The bond-stretching force constants of both bond species show a nearly linear composition dependence between the values of GaP and InP. In contrast, the corresponding Einstein frequencies are different for the two bond species over the whole compositional range. Furthermore, we demonstrate that the composition dependence of bond-stretching force constants and Einstein frequencies for (In,Ga)P, (In,Ga)As, and Zn(Se,Te) is mostly caused by the associated bond length changes. Remaining deviations may be explained by coupling effects between different bond species within the alloy.

Pressure and composition dependence of thermodynamic properties of zinc-blende AlyGa1-yAs alloy

The moment method in statistical mechanics is applied to study the thermodynamic properties of the zinc-blende AlyGa1-yAs compound. The lattice parameter, isothermal bulk modulus, specific heats at the constant volume and constant pressure of the zinc-blende AlyGa1-yAs crystal are investigated in detail as functions of pressure and Al composition up to 10 GPa at room temperature. Numerical calculations have been performed using the many-body Pearson-Takai-Halicioglu-Tiller potential to describe atomic interactions in the AlyGa1-yAs system. Our work shows that the lattice parameter and specific heats of the AlyGa1-yAs alloy increase almost linearly with the Al composition. Nevertheless, when pressure goes up, while lattice parameter and specific heats decrease gradually, the isothermal bulk modulus increases drastically. Present results can be used as reference data for future experiments and theoretical works. Furthermore, this research proposes the potential of statistical moment method on investigation of thermodynamic and mechanical properties of ternary alloys.

Band Structure, Charge Distribution and Optical Properties of AlPxSb1-x Ternary Semiconductor Alloys

The present contribution studies on the composition dependence of the electronic and optical properties of the zinc-blende alloy system AlPxSb1-x. The calculations are performed using a pseudopotential approach under the virtual crystal approximation. Features such as electronic band structure, energy band-gaps, refractive index, dielectric constants and valence and conduction charge densities are determined and their compositional dependence are examined and discussed. The aim of this paper is to provide new data for electronic and optical properties by varying the alloy composition x and to see to what extent the compositional disorder affects the properties of interest. The effect of alloy disorder on the energy band-gaps and electron charge densities is found to be important for getting a meaningful agreement with experiment. Our results show a direct-band gap bowing parameter of 2.7 eV which agrees very well with experiment. Moreover, a transition between indirect band gaps is found to occur twice. Besides, bonding and ionicity are discussed in terms of electron charge distribution. The information derived from the present study can be useful for optoelectronics applications.

Structural, electronic, optical, thermodynamic and elastic properties of the zinc-blende AlxIn1-xN ternary alloys: A first principles calculations

The structural, electronic, optical and thermodynamic properties of the AlxIn1-xN (x = 0, 0.25, 0.50, 0.75 and 1) ternary alloys were investigated using the full potential linearized augmented plane wave (FP-LAPW) method in the framework of density functional theory (DFT). Optimized lattice parameter, bulk modulus and its pressure derivative were determined from suitable fit of the total energy versus volume with Murnaghan equation of state (EOS) for all considered alloys. Variations of the lattice parameter and bulk modulus with the Al concentration (x) deviate from Vegard’s law. Electronic band structure, dielectric function and refractive indices were investigated and computed for the considered alloys. It is found that the variations of the band gap, the static dielectric constant and static refractive index versus the Aluminum Al concentration obey to a quadratic polynomial. Temperature and pressure dependencies of the Gibbs free energy G, isochoric heat capacity CV, entropy S and Debye temperature θD were investigated via the Debye quasi-harmonic model for the Al0.5In0.5N ternary alloy. Furthermore, the elastic constants Cij, the bulk modulus B, Shear modulus G with Young modulus E and the Poison’s ratio v with the compressibility B/G were carried out in the cubic phase. Deduced results agree well with the available theoretical and experimental results.

Structural and elastic properties of zinc-blende and wurtzite InN1-Bi alloys

Structural and elastic properties of InN1-xBix alloys in both zinc-blende and wurtzite phases are studied by using first-principle calculations. Two different Bi-atom arrangements of uniform and clustered configurations have been considered for x = 0.25, 0.5, and 0.75. It is found that clustered configuration has a significant effect on lattice parameters of wurtzite InN1-xBix alloys. A slightly sublinear dependence on the alloy content, x, can be accepted for C11, C12, C13, and C33 in zinc-blende InN1-xBix, and for C12, C13, and C44 in wurtzite InN1-xBix, whereas clearly linear deviations are obtained for C44 and C66 in zinc-blende alloys and for C11 and C33 in wurtzite alloys. The effect of Bi atoms clustering leads to a decrease in all elastic constants and bulk modulus in zinc-blende InN1-xBix, and makes big deviations from Vegard's-like law and has little influence on bulk modulus in wurtzite InN1-xBix alloys.

First-principles calculation of structural, optoelectronic properties of the cubic AlxGayIn1-x-y N quaternary alloys matching on AlN substrate, within modified Becke–Johnson (mBJ) exchange potential

A theoretical study of zinc-blende quaternary alloys AlxGayIn1-x-y N (x=0.343, 0.468, 0.593 and y=0.375, 0.5, 0.625) grown on AlN substrate where the lattice match condition is 〈ABS−P〉y=1,25(1−x). The full-potential linearized augmented plane wave method (FP-LAPW) was used to determine the variations in the bandgap as well as the optical properties. The generalized gradient approximation of Wu and Cohen (WC-GGA) was employed for the exchange-correlation potential to calculate the structural properties and the modified Becke–Johnson potential (TB-mBJ) employed for greater generation of the band gap and the optical properties. The structural properties (lattice parameters and bulk modulus) were assessed for binary, ternary and quaternary compounds. Whenever possible, results were compared with experiments and calculations completed with other computational schemes. The theoretical study of the optoelectronic properties demonstrate that these materials are applicable for optical device working in UV spectrum.

Compound semiconductor alloys: From atomic-scale structure to bandgap bowing

Compound semiconductor alloys such as InxGa1−xAs, GaAsxP1−x, or CuInxGa1−xSe2 are increasingly employed in numerous electronic, optoelectronic, and photonic devices due to the possibility of tuning their properties over a wide parameter range simply by adjusting the alloy composition. Interestingly, the material properties are also determined by the atomic-scale structure of the alloys on the subnanometer scale. These local atomic arrangements exhibit a striking deviation from the average crystallographic structure featuring different element-specific bond lengths, pronounced bond angle relaxation and severe atomic displacements. The latter, in particular, have a strong influence on the bandgap energy and give rise to a significant contribution to the experimentally observed bandgap bowing. This article therefore reviews experimental and theoretical studies of the atomic-scale structure of III-V and II-VI zincblende alloys and I-III-VI2 chalcopyrite alloys and explains the characteristic findings in terms of bond length and bond angle relaxation. Different approaches to describe and predict the bandgap bowing are presented and the correlation with local structural parameters is discussed in detail. The article further highlights both similarities and differences between the cubic zincblende alloys and the more complex chalcopyrite alloys and demonstrates that similar effects can also be expected for other tetrahedrally coordinated semiconductors of the adamantine structural family.

Percolation-type multi-phonon pattern of Zn(Se,S): Backward/forward Raman scattering and ab initio calculations

We perform a combined backward/near-forward Raman study of the multi-oscillator Zn(Se,S) zincblende alloy with particular attention to the transverse optical modes. Besides the three [1×(Zn–Se), 2×(Zn–S)] known modes apparent in backscattering, one novel Zn–Se mode is revealed in near-forward scattering, suggesting a four-mode [2×(Zn–Se), 2×(Zn–S)] percolation behavior (1-bond→2-mode) for Zn(Se,S). The latter four-mode pattern appears to violate most admitted rules behind the current version of the percolation scheme for a zincblende- or diamond-type alloy, in reference to Ga(As,P) and (Ge,Si), respectively, concerning (i) the number of Raman modes, and the composition dependence of their (ii) frequencies and (iii) intensities. It is explained within a refined version of the percolation scheme, now suggested, in which the 1-bond→2-mode behavior is echoed among all constituent bonds of an alloy – referring to (i), the phonon dispersion is taken into account besides the local strain – referring to (ii), and both the Zn–Se and Zn–S bonds exhibit an unusual sensitivity to their local environment at the second-neighbor scale – referring to (iii). The discussion is supported by ab initio phonon calculations using prototype (S,Se)-impurity motifs, and by a contour modeling of the multi-phonon-polariton Zn(Se,S) near-forward Raman spectra within the formalism of the linear dielectric response, based on ellipsometry measurement of the Zn(Se,S) refractive index. Particular attention is awarded to the coupling of neighboring transverse optical modes via their developing transverse electric field when entering the phonon-polariton regime.

Inapplicability of Martin transformation to elastic constants of zinc-blende and wurtzite group-III nitride alloys

The applicability of the Martin transformation [R. M. Martin, Phys. Rev. B 6, 4546 (1972)] to the elastic constants of wurtzite and zinc-blende group-III nitride alloys is examined using density functional theory calculations. The composition dependencies of the elastic constants in InGaN, AlGaN, and InAlN are determined by means of ab-initio calculations and compared with the results obtained from the Martin's method. A detailed analysis reveals that the Martin transformation can approximate reasonably well the dependence of the elastic constants on composition in wurtzite InGaN alloys, except for the case of C33 where it predicts too small bowing. However, it fails to reproduce correctly the composition dependencies of C13 and C33 in wurtzite InAlN and C13, C33, and C44 in wurtzite AlGaN. In order to identify the origin of the failure of the Martin transformation, the effective elastic constants of strained wurtzite alloys with the ideal value of the lattice axial ratio c/a have been investigated. It is shown that these effective elastic constants are significantly closer to the elastic constants predicted by the Martin's method which indicates that the breakdown of the Martin transformation in group III nitride alloys is partially caused by the deviation of the c/a axial ratio from the ideal value.

Near-forward Raman study of a phonon-polariton reinforcement regime in the Zn(Se,S) alloy

We investigate by near-forward Raman scattering a presumed reinforcement of the (A-C,B-C)-mixed phonon-polariton of a A1-xBxC zincblende alloy when entering its longitudinal optical-like (LO-like) regime near the Brillouin zone centre Γ, as predicted within the formalism of the linear dielectric response. A choice system to address such issue is ZnSe0.68S0.32 due to the moderate dispersion of its refractive index in the visible range, a sine qua non condition to bring the phonon-polariton insight near Γ. The LO-like reinforcement regime is actually accessed by using the 633.0 nm laser excitation, testified by the strong emergence of the (Zn-Se,Zn-S)-mixed phonon-polariton at ultimately small scattering angles.

Lattice dynamics of the model percolation-type (Zn,Be)Se alloy: Inelastic neutron scattering,ab initiostudy, and shell-model calculations

The random Zn${}_{1\text{\ensuremath{-}}x}$Be${}_{x}$Se zincblende alloy is known to exhibit a peculiar three-mode [$1\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}$(Zn-Se),$2\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}$(Be-Se)] vibration pattern near the Brillouin zone (BZ) center, of the so-called percolation type, apparent in its Raman spectra. This is due to an unusually large contrast between the physical properties (length, ionicity) of the constituting bonds. In the present work, the inelastic neutron scattering is applied to study the dispersion of modes away from the BZ center, with special attention to the $\stackrel{P\vec}{q}$ dependence of the BeSe-like transverse optic doublet. The discussion is supported by calculations of lattice dynamics done both ab initio (using the siesta code) and within the shell model. The BeSe-like doublet is found to survive nearly unchanged throughout the BZ up to the zone edge, indicating that its origin is at the ultimate bond scale. The microscopic mechanism of splitting is clarified by ab initio calculations. Namely, the local lattice relaxation needed to accommodate the contrast in physical properties of the Zn-Se and Be-Se bonds splits the stretching and bending modes of connected, i.e., percolativelike, (Be-Se) bonds.

Near-forward Raman scattering by bulk and surface phonon-polaritons in the model percolation-type ZnBeSe alloy

We study the bulk and surface phonon-polaritons of the Zn0.67Be0.33Se zincblende alloy by near-forward Raman scattering. The short (Be-Se) bond exhibits a distinct percolation doublet in the conventional backscattering Raman spectra, corresponding to a three-mode behavior in total [1×(Zn-Se), 2×(Be-Se)] for Zn0.67Be0.33Se. This offers an opportunity to achieve a refined understanding of the phonon-polariton modes of a zincblende alloy beyond the current two-mode approximation, corresponding to a [1×(Zn-Se), 1×(Be-Se)] description in the present case. The discussion is supported by contour modeling of the Raman signals of the multi-mode bulk and surface phonon-polaritons within the formalism of the linear dielectric response.

GeSi Raman spectra vs. local clustering/anticlustering: Percolation scheme and ab initio calculations

We formalize within the percolation scheme that operates along the linear chain approximation, i.e., at one dimension (1D), an intrinsic ability behind Raman scattering to achieve a quantitative insight into local clustering/anticlustering in an alloy, using GeSi as a case study. For doing so, we derive general expressions of the individual fractions of the six GeSi percolation-type oscillators [1×(Ge-Ge), 3×(Ge-Si), 2×(Si-Si)], which monitor directly the Raman intensities, via a relevant order parameter κ. This is introduced by adapting to the 1D oscillators of the GeSi-diamond version of the 1D-percolation scheme, i.e., along a fully consistent 1D treatment, the approach originally used by Verleur and Barker for the three-dimensional (3D) oscillators of their 1D-cluster scheme applying to zincblende alloys [H. W. Verleur and A. S. Barker, Phys. Rev. 149, 715 (1966)], a somehow problematic one in fact, due to its 3D–1D ambivalence. Predictive κ-dependent intensity-interplays between the Ge0.5Si0.5 Raman lines are confronted with existing experimental data and with ab initio Raman spectra obtained by using (32-atom) disordered supercells matching the required κ values, with special attention to the Ge-Si triplet and to the Si-Si doublet, respectively.

Spinodal decomposition ranges of wurtzite and zinc blende ZnBVIxO1−x (BVI=S, Se, Te) alloys

Spinodal decomposition ranges of wurtzite and zinc blende ZnBVIxO1−x (BVI=S, Se, Te) alloys from 0°C to 1000°C are represented. The strain energy was estimated in the framework of the valence force field model. All considered alloys have the very extensive decomposition zones in spite of the coherency strain energy. Spinodal decomposition in wurtzite alloys should occur in planes with an orientation that depends on the lattice parameters, stiffness coefficients and composition. Zinc blende alloys posses the larger zones and decomposition should take place only in the {100} oriented planes. Spinodal decomposition ranges are 0.02<x<0.993, 0.026<x<0.994 and 0.045<x<0.987 for wurtzite ZnSxO1−x, ZnSexO1−x and ZnTexO1−x, respectively, at RT.

THE COMPOSITION EFFECT ON THE BOWING PARAMETER IN THE CUBIC TlxAl1-xAs

The band gap bowing parameter of the new semiconductor Tl x Al 1-x As alloys are investigated numerically based on first-principles calculations and the local density approximation. A 16-atom supercell is used to model for the ternary Tl x Al 1-x As alloys. The alloy's lattice constants obey Vegard's law well. Band gap bowing coefficients show very strong composition dependence. The results suggest that the unstrained band gap bowing parameter of the ternary Tl x Al 1-x As alloys is b = 1.9754 eV. The results also suggest that the composition-dependent band gap energy of the zincblende alloys can be expressed by a third-order polynomial equation, Eg(x) = -7.2064x3 + 14.8397x2-10.016x + 2.2217 eV .