Elastic modulus,optical phonon modes and polaron properties in Al1−xBxN alloys

The results of first-principles plane-wave-based pseudopotential method calculations of the elastic modulus, optical phonon modes, and polaron properties of zinc-blende Al_1?xB_xN are presented. Good agreement is obtained with the exciting experimental data for AlN and BN compounds. Our results provide predictions for the remaining mixed crystals Al_1?xB_xN (0 < x < 1) for which no direct experimental or theoretical data are presently available. The compositional dependence of features such as elastic constants and their related mechanical parameters, phonon frequencies, dielectric constants, and polaron parameters was investigated. The study may be useful for the characteristic analysis of AlBN-based quantum well devices.     

Investigation of defect-related optical properties in AlxInyGa1−x−yN quaternary alloys with different Al/In ratios

Al_xIn_yGa_1?x?yN quaternary alloys with different ratios of Al/In were grown by metal-organic chemical vapor deposition on GaN/Al₂O₃ substrates. The structural and emission properties of the as-grown samples were investigated, respectively, by high-resolution X-ray diffraction and photoluminescence (PL) measurements. The PL emission character is related to the two prominent quenching bands, which have been determined to be located at around 1.1 eV and 1.7 eV above the valence band, respectively, by the method of optical quenching of photoconductivity. PL emission is most intense when the Al/In ratio is 7.5 for the Al_xIn_yGa_1?x?yN layer. In addition, a stronger quenching phenomenon with Al/In ratio of 5.0 in Al_xIn_yGa_1?x?yN is observed in accordance with a reduction of the intensity of Al_xIn_yGa_1?x?yN-related emission peak.     

Recombination of nonequilibrium current carriers in n-InAs1−x−ySbxPy

The stationary photoconductivity, the photomagnetic effect, and the relaxation kinetics of photoconductivity in n-InAs_1–x–ySb_xP_y crystals (x=0.06, y=0.11) with n₀ = 8·10¹⁵ and 3·10¹⁶ cm^–3 were measured and the lifetimes of nonequilibrium current carriers in the temperature interval T=78–295 K were determined. The possible mechanisms of recombination, which limit the lifetimes (radiative _R, Auger recombination _A, and recombination through centers with E_f=0.13 eV), which, as is demonstrated, are determined by interband recombination processes with _RA = _RA/(_R + _A), are calculated theoretically. The contribution of the 0.13 eV recombination centers can be significant when n₀10¹⁴ cm^–3.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 52–54, April, 1991.     

Structural and electronic properties of zincblende phase of Tl x Ga1−x As y P1−y quaternary alloys: First-principles study

Using the first-principles band-structure method, we have calculated the structural and electronic properties of zincblende TlAs, TlP, GaAs and GaP compounds and their new semiconductor Tl _x Ga_1?x As _y P_1?y quaternary alloys. Structural properties of these semiconductors are obtained with the Perdew and Wang local-density approximation. The lattice constants of Tl _x Ga_1?x As, Tl _x Ga_1?x P ternary and Tl _x Ga_1?x As _y P_1?y quaternary alloys were composed by Vegard’s law. Our investigation on the effect of the doping (Thallium and Arsenic) on lattice constants and band gap shows a non-linear dependence for Tl _x Ga_1?x As _y P_1?y quaternary alloys. The band gap of Tl _x Ga_1?x As _y P_1?y , E _g (x, y) concerned by the compositions x and y. To our awareness, there is no theoretical survey on Tl _x Ga_1?x As _y P_1?y quaternary alloys and needs experimental verification.     

Studies on the complex behavior of optical phonon modes in wurtzite (ZnO)1−x (Cr2O3) x

This paper reports on the use of phonon spectra obtained with laser Raman spectroscopy for the uncertainty concerned to the optical phonon modes in pure and composite ZnO_1?x (Cr₂O₃) _x . Particularly, in previous literature, the two modes at 514 and 640 cm^?1 have been assigned to ZnO are not found for pure ZnO in our present study. The systems investigated for the typical behavior of phonon modes with 442 nm as excitation wavelength are the representative semiconductor (ZnO)_1?x (Cr₂O₃) _x (x = 0, 5, 10 and 15 %). Room temperature Raman spectroscopy has been demonstrated polycrystalline wurtzite structure of ZnO with no structural transition from wurtzite to cubic with Cr₂O₃. The incorporation of Cr³⁺ at most likely on the Zn sub-lattice sites is confirmed. The uncertainty of complex phonon bands is explained by disorder-activated Raman scattering due to the relaxation of Raman selection rules produced by the breakdown of translational symmetry of the crystal lattice and dopant material. The energy of the E ₂ (high) peak located at energy 53.90 meV (435 cm^?1) due to phonon–phonon anharmonic interaction increases to 54.55 meV (441 cm^?1). A clear picture of the dopant-induced phonon modes along with the B ₁ silent mode of ZnO is presented and has been explained explicitly. Moreover, anharmonic line width and effect of dislocation density on these phonon modes have also been illustrated for the system. The study will have a significant impact on the application where thermal conductivity and electrical properties of the materials are more pronounced.     

Electronic and optical properties of ZnS x Se1−x alloys

A series of calculations from first principles have been carried out to study structural, electronic, and optical properties of ZnS_xSe_1−x alloys. Our results show that the lattice constant scales linearly with sulfur composition. The imaginary parts of the dielectric function are calculated, which are in good agreement with the experimental data. We have also interpreted the origin of the spectral peaks on the basis of band structure and density of states. Additionally, we find that no bowing effect in the absorption edge is observed, unlike other II-VI semiconductor alloys.      

Structural and electronic properties of GaN x As1−x alloys

The structural and electronic properties of cubic GaN _x As_1−x with N-concentration varying between 0.0 and 1.0 with step of 0.25 were investigated using the full potential–linearized augmented plane wave (FP-LAPW) method. We have used the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used for the band-structure calculations. The structural properties of the binary and ternary alloys were investigated. The electronic band structure, total and partial density of states as well as the electron charge density were determined for both the binary and their related ternary alloys. The energy gap of the alloys decreases when we move from x=0.0 to 0.25; then it increases by a factor of about 1.8 when we move from 0.25 to 0.5, 0.75 and 1.0 using EVGGA. For both LDA and GGA moving from x=0.0 to 0.25 causes the band gap to close, showing the metallic nature of the GaN_0.25As_0.75 alloy. When the composition of N moves through x=0.25, 0.5, 0.75 and 1, the band gap increases.     

Pressure effect on the structural,electronic and optical properties of the cubic triangular quaternary BNxAsyP1−x−y alloys: First principle study

Predicted results of the structural, electronic and optical properties of the cubic zinc-blende phase of BN, BAs and BP binary compounds and their related ternary and quaternary alloys are presented. The density functional theory (DFT) within full potential linearized augmented plan wave (FP-LAPW) is employed. Different exchange correlation approximations were used to calculate the structural properties as well as the total energies, lattice parameters, bulk modulus and its first pressure derivative. The electronic band structures were treated with the local density approach and Tran Blaha modified Beck-Johnson (TB-mBJ) approximation. A quadratic fit of the lattice parameter, bulk modulus and band gap was performed, where a nonlinear variation with the composition x and y is found. Moreover, the optical properties have been investigated, where the dielectric behavior, the refractive index variations and the loss energy were studied. Furthermore, the electronic and optical properties were computed under hydrostatic pressure. Our results showed great agreement with the previous available experimental and theoretical data found in the literature.     

Energy gap and optical dielectric constant of Pb1−xCdxSe films

The transmission spectra of laser-deposited Pb_1−xCd_xSe films (x = 0, 0.02, 0.05, 0.08 and 0.12) have been measured over the energy range 0.1–0.65 eV at two different temperatures 90 and 300 K. From these spectra the dispersion of the refractive index and the absorption coefficient-energy dependence have been obtained. Thus the dependences of the gap and the optical dielectric constant on the Cd content x have been investigated. The experimental results have been discussed in the framework of the recently developed theoretical model by Volkov and Pankratov et al^1,2.     

Concentration-dependent crystal structure,elastic constants and electronic structure of Zr x Ti1−x alloys under high pressure

The physical properties of ZrxTi1-x（x=0.0, 0.33, 0.5, 0.67, 0.75 and 1.00） alloys were sinmlated by virtual crystal approximation （VCA） methods which is generally used for disordered solid solutions modeling. The elastic constant, electronic structure and thermal Equation of state （EOS） of disor- dered ZrxTi1-x alloys under pressure are investigated by plane-wave pseudo-potentia1 method. Our simulations reveal increasement of variations of the calculated equilibrium volumes and decrease- ment of Bulk modulus as a function of the alloy compositions. Lattice parameters a and c of alloys with differentZr concentrations decrease linearly with pressure increasing, but the c/avalues are increasing as pressure increases, indicating no phase transitions under pressure from 0 GPa to 100 GPa. The elastic constants and the Bulk modulus to the Shear modulus ratios （B/G） indicate good ductility of Zr, Zr0.33 Ti0.67 Zr0.5Ti0.5, Zr0.75Ti0.25 and Ti, but the Zr0.67Ti0.33 alloy is brittle under 0 K and 0 GPa. The metallic behavior of these alloys was also proved by analyzing partial and total DOS.     

Magnetostriction of amorphous GdxAg1−x alloys

Magnetostriction measurements above 4.2 K and up to 2.2 T have been performed in the amorphous alloys Gd_xAg_1−x (0.30 ⩽ x ⩽ 0.40). Magnetostriction is purely of volume character. It shows with composition a maximum at x = 0.35, and this behaviour can be explained if forced volume magnetostriction derives form the strain dependence of the two-ion longitudinal spin correlation. The isotropic spin exchange correlation seems irrelevant in these series, as also put forward by thermal expansion measurements.     

Magnetic and electric properties of Yb x Mn1 − x S alloys

Results from investigating the structural, magnetic, and electrical properties of Yb _x Mn_{1 ? x} S alloys (0 ≤ x ≤ 0.2) synthesized on the basis of manganese monosulfide are presented. Substituting manganese for ytterbium increases the concentration of charge carriers and lowers the activation energy. The observed anomalies in the temperature dependence of resistivity are explained by an impurity semiconductor model with donor 4f levels.     

Structural,optical and transport properties of PbxHg1−xTe alloys

It has been shown that the plasma frequency for polycrystalline PbxHg_1−xTe samples with x = 0.93 and x = 0.85 decreases unexpectedly compared with that of pure high-quality PbTe. At the same time the free-carrier concentration is lower than for the high-quality single-crystal samples of pure PbTe treated in the literature.     

Elastic constants of the alloys Cd1−x Zn x (x<0.3%) and their temperature dependence

The temperature dependence of elastic constants of Cd_1–x Zn _x alloys, havingx=0.021, 0·042 and 0·233 at.%, has been measured in the temperature range from 4·2 to 300 K by the pulse-echo-overlap ultrasonic method. The adiabatic compressibilities and the Debye temperatures have been calculated. All elastic constants with the exception ofc ₄₄ increase slightly with the growing concentration of Zn.The summary of this paper was presented on the 7^th Conference on Ultrasonic Methods in ilina, September 11^th–13^th, 1980.     

On the nature of a lattice vibrational mode at a frequency of 135 cm−1 in Hg1 − x Cd x Te alloys

The vibrational spectrum of a cadmium impurity atom in the HgTe crystal has been calculated using the microscopic theory of lattice dynamics in the approximation of a low impurity concentration. Within this theory, the behavior of the local and quasi-local modes induced upon substitution of the lighter Cd atom for the Hg atom in the region of the zero or very low one-phonon density of states in the HgTe crystal has been considered. It has been found that, apart from the local mode at a frequency of 155 cm^?1, the calculated vibrational spectra exhibit a weak (but clearly pronounced) feature at a frequency of 134 cm^?1, which coincides with the experimentally observed vibrational mode (the “minicluster” mode) at a frequency of 135 cm^?1 in the Hg_{1 ? x} Cd _x Te (x = 0.2–0.3) alloys at 80 K.     

Synthesis,microstructure and dielectric properties of (1−x)PSN−xPLuN

Ceramic lead niobates and their solid solutions PSN–PLuN (pure lutecium niobate) were synthesized by solid state reactions. The sequence of phases formed at PSN–PLuN synthesis has been studied by X-ray analysis. Their symmetry changed from rhombohedral for PSN to pseudo-monoclinic for the 0.75PSN–0.25PLuN compositions. The performed EDS investigations revealed that the samples PSN–PLuN are perfectly sintered. They contain a little glassy phase and their grains are well shaped. The increase of lutecium content in the examined solid solution caused downward shift of the temperature of the phase transition. The decrease of the achieved permittivity values ? was observed as well.     

Structural,transport and some optical properties of PbxPt1−xTe alloys

A solid solution of PtTe in PbTe was investigated. The method of preparing crystalline samples using the Czochralski procedure is described. A detailed microprobe analysis was also made. The transport properties in the 10–300 K range and the room temperature reflectivity coefficient in the FIR range were measured. Free-carrier mobility at room temperature was 0.12m²V⁻¹s⁻¹, but at 15K it increased to a value of about 14 m² V⁻¹s⁻¹. The optical results indicated that the plasma frequency was lower (and had moved into the FIR range) compared with the value for pure PbTe.     

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMn_xFe_1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ₀(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ ₀ ^m ∼220 μΩ cm at x _C∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 193–197. Original Russian Text Copyright ? 2002 by Kourov, Korotin, Volkova.     

Calculation of the temperature dependence of the thermal emf in amorphous alloys CaxAl1−x and AuxNi1−x

The temperature dependence of the thermal emf of Ca_xAl_1–x and Au_xNi_1–x for four different concentrations of the components of the alloys is calculated on the basis of the concept of dynamic concentrated excitations in amorphous metal systems. It is shown that increasing x from 0.15 to 0.50 in Au_xNi_1–x raises the thermal emf, and a further increase in the Au concentration from 0.50 to 0.80 lowers S(T). For Ca_xAl_1–x the dependence S(T) is calculated in the interval of Ca concentrations from 0.55 to 0.75. In this concentration interval the thermal emf decreases as x is increased. It is shown that for both types of alloys the S(T) curve bends abruptly at a temperature near 10T₀ (where T₀ is the concentration-dependent characteristic temperature of amorphous alloys separating the ranges of strong and weak scattering of electrons by dynamic concentration excitations). The so-called S(T) knee shifts toward lower temperatures when the thermal emf increases with increasing x and toward higher temperatures when S(T) decreases with increasing x. The results agree with experimental data.Institute of Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 43–48, August, 1994.