Determination of the Melt Undercooling Required for Producing Al x Ga y In1 – x – y Sb1 – z Bi z /InSb Heterostructures

Conditions for temperature-gradient epitaxial growth of Al _x Ga _y In_{1 – x – y} Sb_{1 – z} Bi _z /InSb heterostructures are examined. The factors are established which determine the initial melt undercooling required for preventing the thermal degradation of the substrate.     

Growth of Ga x In1 − x As y P1 − y /GaAs quantum dot arrays by ion beam deposition

Experimental data are presented that demonstrate the possibility of producing GaInAsP quantum dots on GaAs by ion beam deposition. The morphology of the quantum dots and the effect of GaAs substrate temperature on parameters of GaInAsP quantum dot arrays have been studied by atomic force microscopy and scanning electron microscopy. We have determined the elemental composition of the quantum dots and obtained photoluminescence spectra of the GaInAsP/GaAs heterostructures.     

Growth and properties of Ga y In1 − y P z As1 − x − z Bi x solid solutions on GaP substrates

Data are presented on temperature-gradient melt growth of GaInPAsBi solid solutions on GaP substrates. Heterophase equilibria in the Ga-In-P-As-Bi system are analyzed in terms of the regular solution model. The growth kinetics, composition, and structural perfection of GaInPAsBi/GaP heterostructures are investigated.     

Indentation fracture in the In1−x Ga x As y P1−y /InP system and its effect on microhardness anisotropy characteristics

Knoop microhardness anisotropy measurements on the {100}-orientated In_1–x Ga _x As _y P_1–y /InP system have disclosed an appreciable variation in hardness behaviour across the composition range of the alloy. This paper relates these variations to changes in the directional fracture characteristics of the system. The qualitative investigation of both Vickers and Knoop indentation fracture has established the emergence of a secondary 100 cleavage direction at high values of the composition parameter, abovey 0.6. Furthermore, the number and extent of cracks emanating from indentations were seen to increase appreciably asy increases from 0 to 1. A quantitative analysis of Vickers indentation fracture in the quaternary system has indicated a marked dependence of fracture-related parameters on both the indentor orientation and composition. Fracture toughness values from 3.10⁵ to 1.10⁶ N m^/12 have been derived using expressions from the literature. The marked change in Knoop microhardness anisotropy characteristics with increasingy in the In_1–x Ga _x As _y P_1–y /InP system has been partially correlated to the emergence of 100 cleavage and the general increase in indentation fracture, highlighted by the quantitative fracture measurements. Thus, it is concluded that even at very low indentation loads, the effect of fracture on the measured hardness of crystalline materials cannot be ignored.     

Effect of the Crystallographic Orientation of GaAs Substrates on the Composition of Ga x In1 – x P Layers

The effect of the crystallographic orientation of GaAs substrates on the composition of Ga _x In_{1 – x} P solid solutions grown by liquid-phase heteroepitaxy is studied. It is shown that GaAs-lattice-matched Ga _x In_{1 – x} P solid solutions can be grown, under identical conditions, on (100), (111), and (111) GaAs substrates using different melt compositions. The results are interpreted in terms of the contribution from the energy of the crystal–melt interface to the total energy of mixing of the solid solution.     

Temperature-Dependent Elastic Constants and Dielectric Properties of (Zn1 – x Cd x )3(P1 – y As y )2 Crystals

Crystals of constant-lattice-parameter (a const) and constant-thermal-expansion ( _a const) (Zn_{1 – x} Cd _x )₃(P_{1 – y} As _y )₂ solid solutions with 0.71 x 0.94 and 0.2 y 1 are prepared, and their elastic and dielectric properties are studied between 78 and 400 K. The elastic constants are found to decrease linearly with increasing temperature and to rise monotonically with increasing Cd and As content, up to x = 0.94 and y = 1. These findings are interpreted in terms of structural changes and bond rearrangement near the morphotropic structural transformation. Dielectric permittivity rises monotonically with temperature and solute concentration and shows a sharp upturn at x = 0.94 andy = 1. The extremely high dielectric permittivity is interpreted in terms of charge transfer between defect complexes responsible for deep levels in the band gap.     

The influence of polarized oscillations on the emission spectrum of a multicascade planar structure based on In x Ga1 − x As/In x Al1 − x As layers

The influence of crystal-lattice oscillations on the spectrum of electron occurring in a cascade of several-nanometer-thick planar layers has been studied. It is shown which phonons affect the emission spectrum of a heterolaser based on this structure, depending on the layer thickness.     

First-principles investigations of structural, elastic, electronic and magnetic properties of Ga1−x Mn x P and In1−x Mn x P

We employ the full-potential linearized augmented plane wave plus local orbital (FP L/APW + lo) method based on the density functional theory (DFT) in order to investigate the structural, elastic, electronic, and magnetic properties of ordered dilute ferromagnetic semiconductors Ga_1?x Mn _x P and In_1?x Mn _x P at (x = 0.25) in the zinc blende phase, using generalized gradient approximation, GGA (PBE). To our knowledge the elastic constants of these compounds have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Results of calculated electronic structures and magnetic properties reveal that both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P have stable ferromagnetic ground state, and they are ideal half-metallic (HM) ferromagnetic at their equilibrium lattice constants. Also we show the nature of the bonding from the charge spin-densities calculations. The calculated total magnetic moments are 4.0 μ_B per unit cell for both Ga_0.75Mn_0.25P and In_0.75Mn_0.25P, which agree with the Slater–Pauling rule quite well, and we observe that p–d hybridization reduces the local magnetic moment of Mn from its free space charge value and produces smaller local magnetic moments on the nonmagnetic Ga, In and P sites. The values of N ₀α and N ₀β exchange constants confirm the magnetic nature of these compounds. From the robust half-metallicity of Ga_0.75Mn_0.25P and In_0.75Mn_0.25P as a function of lattice constant is also investigated.     

Growth and optical properties of In x Ga1−x P nanowires synthesized by selective-area epitaxy

Ternary Ⅲ-Ⅴ nanowires (NWs) cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield,reprodudbility,and tunable optical absorption.Here,we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1-xP NW arrays using metal-organic vapor phase epitaxy and detail their optical properties.A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array.The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy.Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved.Transmission electron microscopy and energy dispersive X-ray measurements performed on crosssection samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis.     

Vapor Growth of Pb1 – x In x Te Crystals

Vapor growth of In-doped PbTe crystals by the sublimation–condensation and vapor–liquid–solid (VLS) processes is examined. Well-faceted Pb_{1 – x} In _x Te crystals with x = 0.04–0.06 are prepared by the sublimation method. The effects of the charge composition on the facial development and growth rate in the range 0 x 0.02 are discussed. The growth process at x 0.02 is shown to follow the VLS mechanism. Bulk Pb_{1 – x} In _x Te crystals with x 0.05 are grown by a vertical VLS process. The crystal composition is shown to depend significantly on the rate of ampule translation through the temperature field of the furnace and the separation between the evaporation and condensation zones. The longitudinal indium profiles in the crystals are correlated with growth kinetics.     

A comparison of strain relief behaviour of In x Ga1− x As alloy on GaAs (001) and (110) substrates

A comparative study on the strain relief behaviour of epitaxially grown In _x Ga_{1 – x} As (where 0.1 × 1) alloys on GaAs (001) and (110) were carried out using transmission electron microscopy (TEM) and high resolution X-ray diffraction (XRD). Three different strain relief mechanisms related to the formation of misfit dislocations (MDs) were observed. The dominant strain relief process can be a single mechanism or a combination of two of the three mechanisms depending on the substrate orientation and the in content.     

Structural Phase Transitions of High-Pressure Li x Na1 – x NbO3 Solid Solutions

Li _x Na_{1 – x} NbO₃ (x = 0.125, 0.17, 0.25) solid solutions are synthesized at high pressures (6 GPa) and temperatures (1100–1500°C), and their polymorphic transformations are studied by x-ray diffraction. The composition and temperature dependences of lattice parameters for the identified polymorphs are presented. The results demonstrate that the high-pressure solid solutions with x = 0.17 and 0.25 are supersaturated under ordinary conditions. Heating these solid solutions to above 800°C leads to precipitation of an LiNbO₃-based phase.     

Crystal Growth and Properties of Cd1 – x Zn x As2 Solid Solutions

Cd_{1 – x} Zn _x As₂ (x = 0.03, 0.05, 0.06) single crystals are grown by the Bridgman method, and their optical absorption spectra are measured. The introduction of Zn is shown to increase the band gap of CdAs₂, by up to 14 meV at x = 0.06. The highest content of ZnAs₂ incorporated into CdAs₂ is 6 mol %.     

Relaxor Behavior of Pb[(Mg0.5W0.5 )1 – x Ti x ]1 – y Sn y O3 Ceramics

The dielectric and ferroelectric properties of Pb[(Mg_0.5W_0.5)_{1 – x} Ti _x ]_{1 – y} Sn _y O₃ (x = 0.4–0.5, y = 0–0.15) solid solutions are studied. The results are used to elucidate the origin of the relaxor state developing in a temperature range between the para- and ferroelectric phases.     

Electronic and optical properties of (Al x Ga1−x )1−y Mn y As single crystal: a new candidate for integrated optical isolators and spintronics

We have explored the electronic and optical properties of cubic (Al _x Ga_1?x )_1?y Mn _y As system using the FP-LAPW method. The unit cell has 64 atoms, so that one manganese (Mn) atom is placed in the position of gallium site, which corresponds to 3.125 % doping concentration with x = 12.5 %. Our calculations, using local density approximation + U (Hubbard parameter) scheme, predict that the ferromagnetic state for AlGaMnAs, with a magnetic moment of about 4.014 μ_B per Mn dopant is more favorable. Despite its electronic properties being strongly affected by inducing small amounts of Mn substitutional atoms in the cationic sublattice of AlGaAs, (Al _x Ga_1?x )_1?y Mn _y As possesses optical properties strictly less than those of Al _x Ga_1?x As, especially its optical conductivity at the peak 1.256 eV. The results indicate that AlGaMnAs may be a good candidate for optoelectronics when exploited in optical fiber networks, and it can still be of great interest because of its promising potential when used for spintronics.     

Structural transformations in amorphous As x Se1−x (0 ≤ x ≤ 0.20) films

Structural transformations are examined by the employment of Raman scattering measurements for amorphous Se-rich As _x Se_1−x (0 ≤ x ≤ 0.2) alloys. It is found that the molecular structure of amorphous Se (a-Se) on the scale of medium-range order differs from the structure of most inorganic glasses and may be placed between 3-dimensional network glasses and polymeric ones. Further experiments show the existence of successive phases in laser-induced glass—crystalline transition with pronounced threshold behavior. By comparing peak width, peak location and Raman intensity in the range of bond modes it is derived that the changes occur not monotonically with increasing As content. The composition-induced changes of the spectra are explained by cross-linking of Se chains. Under laser irradiation, the changes in the optical transmission, holographic recording properties and Raman spectra of amorphous As _x Se_1−x films with 0 < x ≤ 0.2 have been examined. The dependence of the transmissivity and diffraction efficiency on the irradiation energy density shows two qualitatively different regions. Below the energy density threshold, E _th, only small changes in the local structure of the system can be detected. In the low-energy region, transient changes in transmissivity are observed. Qualitative explanation of this behavior may be based on associating such with alternating of deep defect states. Above E _th, the changes were attributed to crystallization transformation. The corresponding Raman spectra reveal transformation of the system from amorphous into the crystalline phase under laser irradiation. Although several articles and texts have provided reviews on various properties and applications of chalcogenide glasses, there is no thorough study of local atomic structure and its modification for Se-rich amorphous As _x Se_1−x . The present paper is concerned with this problem.     

Peculiarities of the Current–Voltage Characteristic of n-GaP–p-(InSb)1 – x(Sn2)x Heterostructures

Technical Physics Letters - The current–voltage (I–V) characteristics of n-GaP–p-(InSb)1 – x(Sn2)x (0 ≤ x ≤ 0.05) heterostructures have been studied. At low...     

Theoretical prediction of structural parameters, band-gap energies, and mixing enthalpies of Sc1−x In x As alloys

Structural parameters, band-gap energies, and mixing enthalpies of Sc_1?x In _x As alloys were calculated using the full-potential linearized–augmented plane wave method. These calculations are based on density functional theory, within local density approximation, and generalized gradient approximation for the exchange and correlation potential. Given that the binary precursor compounds ScAs and InAs crystallize in rock-salt and zinc-blende, respectively, we made calculations for the ternary alloys in these two phases. The effect of composition x on structural parameters, band-gap energies, and mixing enthalpies was analyzed for x = 0, 0.25, 0.5, 0.75, 1. The effect of atomic composition on lattice constant, bulk modulus, and band-gap energy shows nonlinear dependence on concentration x. Deviations of the lattice constant from Vegard’s law and deviations of the bulk modulus and gap-energy from linear concentration dependence were found. We have found a metallic character for rock-salt Sc_1?x In _x As alloys, while the zinc-blende Sc_1?x In _x As alloys are semiconductors. Our results show that the band-gap undergoes a direct ( $X \rightarrow X$ )-to-direct ( $\Upgamma\rightarrow \Upgamma$ ) transition at a given indium composition. The physical origin of the band-gap bowing in zinc-blende Sc_1?x In _x As alloys was investigated. To study the thermodynamic stability of Sc_1?x In _x As alloys, a regular-solution model was used. This resulted in lower mixing enthalpies for zinc-blende Sc_1?x In _x As alloys.     

Electrical Properties of Cd x Zn1 – x As2 Solid Solutions at Pressures of up to 9 GPa

The electrical properties of n-type Cd_0.97Zn_0.03As₂ and Cd_0.95Zn_0.05As₂ single crystals are studied at hydrostatic pressures of up to 9 GPa. With increasing pressure, the carrier concentration in the solid solutions increases by more than three orders of magnitude, while their electrical resistivity drops by more than four orders of magnitude. In contrast to CdAs₂, the pressure dependences of resistivity for the solid solutions show no anomalies, which is interpreted as evidence that Zn consolidates the structure of CdAs₂, occupying vacant As sites.     

Perovskite La1?x Sr x Ga1?y Mn y O3 solid solution crystals: Raman spectroscopy characterization

The first-order orthorhombic–rhombohedral phase transition of La_1−x Sr _x Ga_1−y Mn _y O₃ (LSGMn) crystals is studied by Raman spectroscopy. An increase in Mn content causes significant changes in Raman spectra, especially in the high-wavenumber spectral range. The Raman spectrum of La_1−x Sr _x Ga_1−y Mn _y O₃ compound with x = y = 0.02 is dominated by MnO₆ internal vibrations. Moreover, a change in the spectrum of this crystal is observed when the 785-nm excitation line is used. Essential reduction in the number of Raman modes during the phase transition is experimentally observed. The temperature of the phase transition decreases with increasing Sr and Mn contents, at the rate of about 20 K/at%.