Showing papers on "Lattice constant published in 1985"

GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications

Abstract: The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

Stabilization of bcc Co via epitaxial growth on GaAs.

Abstract: A new metastable phase of cobalt---body-centered cubic---has been synthesized by use of molecular-beam epitaxial growth to stabilize the crystal structure. Large (1\ifmmode\times\else\texttimes\fi{}1 ${\mathrm{cm}}^{2}$) films have been grown on (110) GaAs and characterized by high-energy electron diffraction, Auger analysis, x-ray diffraction, magnetometry, spin-polarized photoemission, and ferromagnetic resonance. The results indicate a ferromagnetic material very similar to $\ensuremath{\alpha}$-Fe both electronically and magnetically, with a metastable lattice constant ${a}_{0}=2.827$ \AA{}. This technique provides a general approach for the realizing of metastable phases.

Calculation of the surface segregation of Ni-Cu alloys with the use of the embedded-atom method

Abstract: The surface composition of Ni-Cu alloys has been calculated as a function of atomic layer, crystal face, and bulk composition at a temperature of 800 K. The results show that the composition varies nonmonotonically near the surface with the surface layer strongly enriched in Cu while the near-surface layers are enriched in Ni. The calculations use the embedded-atom method [M. S. Daw and M. I. Baskes, Phys. Rev. B 29, 6443 (1984)] in conjunction with Monte Carlo computer simulations. The embedding functions and pair interactions needed to describe Ni-Cu alloys are developed and applied to the calculation of bulk energies, lattice constants, and short-range order. The heats of segregation are computed for the dilute limit, and the composition profile is obtained for the (100), (110), and (111) surfaces for a variety of bulk compositions. The results are found to be in accord with experimental data.

Stresses in semiconductors: Ab initio calculations on Si, Ge, and GaAs.

Abstract: Explicit formulas for the calculation of stress are presented based on the stress theorem and the local-density-functional approximation. Norm-conserving pseudopotentials are applied in a plane-wave basis for calculations on the semiconductors Si, Ge, and GaAs. Besides the lattice constants and bulk moduli, complete sets of elastic constants are given, together with the optical \ensuremath{\Gamma} phonon frequencies and internal-strain parameter \ensuremath{\zeta}. Electronic charge density structure factors, deformation potentials, and strain-induced splittings of phonons are given, as well as the nonlinear third-order elastic constants. Good agreement with experiment is found throughout, except for persistent deviations from the x-ray diffraction values for \ensuremath{\zeta}.

Effect of mismatch strain on band gap in III‐V semiconductors

Abstract: Interfacial elastic strain induced by the lattice parameter mismatch between epilayer and substrate results in significant energy–band‐gap shifts for III‐V alloys. The epilayers used in this study are GaxIn1−xAs on (100) InP and GaxIn1−xP on (100) GaAs prepared by organometallic vapor phase epitaxy. For layer thicknesses between 1 and 1.5 μm, and Δas.f./a0≤3.5×10−3 the misfit strain is assumed to be accommodated elastically. The energy–band‐gap shifts are determined by comparing the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers. A calculation of the energy–band‐gap shift due to biaxial stress made for GaxIn1−xAs is found to agree with the photoluminescence measurements. In addition, a comparison of the energy–band‐gap shift for GaxIn1−xP shows a clearly different dependency for tensile and compressive strain, in good agreement with calculated results.

UFe4P12 and CeFe4P12: Nonmetallic isotypes of superconducting LaFe4P12

Abstract: The new compound UFe4P12, which was found to be isostructural to superconducting LaFe4P12 and have a lattice constant of 7.7729 A, is a semiconductor and shows ferromagnetic order below 3.15 K. CeFe4P12 is also a semiconductor, and its magnetic susceptibility is unusually small in comparison to LaFe4P12. The semiconducting behaviors of both UFe4P12 and CeFe4P12 seem anomalous and may arise from strong f‐electron hybridization.

Calculated ground state properties of light actinide metals and their compounds

Abstract: Agreement between calculated and measured atomic volumes, bulk moduli and cohesive energies of the light actinide metals establishes the combination of self-consistent energy band and density functional theory as an appropriate description of these, the last, transition metals in the periodic table. Similar calculations for NaCl-type compounds of the light actinides are able to explain characteristic trends in lattice constant and bulk modulus. Furthermore, the onset of ferromagnetic ordering and the observed relationship between lattice constant and magnetic moment are, at least qualitatively, given correctly. Relativistic, in particular spin-orbit, effects alter the calculated magnetic properties dramatically being responsible for both large magnetic anisotropy and predominant orbital moments in all magnetic light actinide compounds in which the f electrons are itinerant. The calculated magnetic moments of NaCl-type uranium compounds are, however, only in agreement with experiment when the pairing energy between electrons includes an orbital contribution.

Hybrid electronic properties between the molecular and solid state limits: Lead sulfide and silver halide crystallites

Abstract: Tiny single PbS crystals of ∼25 A diameter are synthesized and studied optically in low‐temperature colloidal solutions. Electron microscopic examination shows a simple cubic rock salt structure with a lattice constant unchanged, within experimental error, from the bulk value. These crystallites lack the near infrared electronic absorption characteristic of bulk PbS. The small crystallite absorbance in the visible rises more steeply than does the bulk absorbance. These results reflect electron and hole localization if one considers the variation in effective mass across the band structure. A simple discussion of localization anywhere in the Brillouin zone is given. For the first time, crystallite syntheses are carried out in solvent mixtures that form transparent glasses upon cooling. The PbS spectra are independent of temperature (at current experimental resolution) down to 130 K, in contrast to earlier results for quantum size exciton peaks in ∼20 A ZnS crystallites. Previously published observations of size dependence in the excited state electronic properties of AgI and AgBr are explained as consequences of electron and hole localization in the small crystallites. AgBr appears to be the first indirect gap semiconductor to be examined in the regime where bulk properties are not fully formed.

Theoretical study of Si/Ge interfaces

Abstract: We present a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides. The self‐consistent calculations, based on the local density functional and ab initio pseudopotentials, determine the minimum energy configurations, and the relative position of the Si and Ge bands. The presence of the strains influences the interface dipole, and also causes significant shifts and splittings of the bulk bands. For (001) interfaces we find for the top of the valence bands: Ev, Ge−Ev, Si=0.74 and 0.21 eV, respectively, for the cases corresponding to Ge strained to match a Si substrate and vice versa. A discussion of these results and comparison with experiment is presented.

Cohesion and structure in stage-1 graphite intercalation compounds

Abstract: We have developed a Thomas-Fermi theory for the structural and elastic properties of the first-stage alkali-metal graphite intercalation compounds We use a simplified model for the electronic structure of these materials which assumes full charge transfer between the alkali metal and the graphite, no hybridization between metal and carbon states, and a uniform distribution of the donated charge on the graphite planes We have computed lattice constants, compressibilities, shear moduli, alkali-metal diffusion constants and activation energies, and domain-wall thicknesses; general agreement with available experiments is found These results indicate that our model of the electronic properties is consistent with known elastic and structural properties The interplane metal-carbon interaction is mostly determined by a competition between Coulomb attraction and hard-core repulsion The Li ion is much more compact than that of K, Rb, or Cs, which explains the higher compressibility of the Li graphite intercalation compound and the lower Li ionic mobility The Na--C bond is found to be very soft, explaining the lack of formation of Na-intercalated graphite The in-plane alkali-metal--alkali-metal interaction is determined almost entirely by the Coulomb interaction, and is thus relatively independent of the alkali-metal species

Lattice parameters of Zn1−xMnxSe and tetrahedral bond lengths in AII1−xMnxBVI alloys

Abstract: This paper reports the results of lattice parameter measurements on the ternary semiconductor alloy Zn1−xMnxSe over the range 0≤x≤0.57. We find that the mean cation‐cation distance increases linearly with manganese concentration x according to Vegard’s Law. It is also noted that this linear dependence occurs across the region in which the alloy changes crystal structure from zinc blende (x≤0.30) to wurtzite (0.33≤x). These observations are compared with the behavior of the crystal lattice as a function of composition in other AII1−xMnxBVI alloys. A fairly unifed pattern of behavior emerges, relating the lattice parameters and bond lengths for the entire family of these materials. In addition, this analysis provides an experimentally determined value of the tetrahedral radius of manganese.

Structural Dependence on Sintering Temperature of Lead Zirconate‐Titanate Solid Solutions

Abstract: Pb(Zr /SUB 0.525/ Ti /SUB 0.475/ )O3 piezoceramics, both unmodified and doped with 2 wt% Bi2O3 or Nb2O5, were prepared by the usual techniques, using sintering temperatures from 900 to 1250C. The microstructural data showed that the sintering temperature which produces minimum porosity is altered by the oxide additions. X-ray diffraction demonstrated the coexistence of both ferroelectric phases. The lattice parameter measurements showed that the tetragonal and rhombohedral unit cells of the two ferroelectric phases depend on the sintering temperature.

Transmission electron microscope and transmission electron diffraction observations of alloy clustering in liquid-phase epitaxial (001) GaInAsP layers

Abstract: Transmission electron microscope examinations performed on liquid‐phase epitaxial GaInAsP layers grown on (001) InP substrates showed a coarse tweed structure (∼150‐nm scale) and a fine granular structure (∼15‐nm scale). Transmission electron diffraction patterns revealed main spots with associated satellite spots, indicating the presence of periodic variations in lattice parameter along the [100] and [010] directions and of wavelength corresponding to the fine granular structure. The particular behavior depended on the alloy layer composition. Both structures are attributed to alloy clustering arising from spinodal decomposition.

Semiconductor device with hole conduction via strained lattice

Abstract: A field-effect transistor includes a conduction channel between a source terminal and a drain terminal, which channel employs holes as the charge carriers. The conduction channel is disposed within a layer of material comprising a group III-V compound of the periodic table and having a crystalline lattice structure which is stressed in two dimensions by means of epitaxial growth upon a thicker and rigid supporting layer comprising a different group III-V compound having a larger lattice spacing. The layer having the conduction channel is relatively thin being on the order of a few electron wavelength in thickness. The stretching of the layer having the conduction channel shift the energy levels of holes therein to remove the degenerate state thereof, thereby elevating light holes to an energy level characterized by increased mobility.

X‐ray double crystal diffraction study of porous silicon

Abstract: Depending on the dopant concentration, two distinct types of porous silicon can be formed during the anodization of silicon in hydrofluoric acid. A range of samples of both types of porous silicon has been investigated using x‐ray double crystal diffraction techniques. The crystal lattice of porous silicon is found to be tetragonally distorted. In the plane of the substrate, the interplanar spacing of the porous film is identical to that of the substrate but is increased in the direction normal to it. The increase is typically 700 ppm in the type of film formed on heavily doped silicon and 6000 ppm in that on lightly doped silicon. We propose that stresses, generated by the growth of a native oxide on the surface of the pores, are responsible for the observed increase in lattice parameter. The different interplanar spacings of the two types of film are related to the observed differences in their oxygen contents which are a consequence of their different surface area to volume ratios.

Strain measurement of epitaxial CaF2 on Si (111) by MeV ion channeling

Abstract: Planar strain in CaF2 films, grown by molecular beam epitaxy at 700 °C on (111) Si substrates, has been measured by MeV 4He+ ion channeling. For CaF2 films thinner than 200 nm, the planar strain was found to be tensile. No strain was observed for films thicker than 200 nm. The observed tensile strain cannot be explained by a simple pseudomorphic growth model since the planar strain would be compressive due to the larger lattice constant of CaF2 relative to Si. A plausible explanation of the results is that defects are nucleated at the growth temperature to relieve stress. These defects then result in a tensile planar strain as the sample is cooled down after growth due to the large difference in thermal expansion coefficients between CaF2 and Si.

CeCu2: a new Kondo lattice showing magnetic order

Abstract: The authors report measurements on the lattice parameter, electrical resistivity, thermal conductivity, thermoelectric power, susceptibility, magnetisation and specific heat as well as preliminary neutron diffraction results for the orthorhombic compound CeCu2. The Ce valence is close to three and the overall crystal-field splitting seems to be approximately=200K. CeCu2 behaves as a Kondo lattice system with a 'Kondo temperature' in the crystal-field ground state being of the order of 10-20K. Below 3.5K CeCu2 shows magnetic order of an anisotropic antiferromagnetic type.

Crystal growth of Cd1−xZnxTe and its use as a superior substrate for LPE growth of Hg0.8Cd0.2Te

Abstract: Cd1−xZnxTe (x=0.04) boules providing wafers with single crystal areas as large as 10 to 12 cm2 have been grown by the vertical modified‐Bridgman (VMB) technique and evaluated as an alternative to CdTe for use as substrates for LPE growth of HgCdTe layers. The CdZnTe crystals, as compared with typical CdTe crystals, exhibit lower defect densities, increased mechanical strength, and significantly improved macro‐ and micromorphologies of LPE layers of HgCdTe grown on them. The surface morphology of LPE layers grown on CdZnTe substrates shows less orientation dependence than for layers grown on CdTe substrates, for orientations close to the {111} planes. The addition of Zn to the CdTe lattice may result in increased covalency and reduced ionicity, which in turn inhibit plastic deformation and generation of dislocations. These factors, combined with the ability to adjust the lattice constant to any desired value within the two extrema, allow the growth of low‐defect density HgCdTe layers required for high‐perf...

Lattice parameter variation and magnetization studies on titanium‐, zirconium‐, and tin‐substituted nickel‐zinc ferrites

Abstract: The variation of lattice parameter, saturation magnetization, and Curie temperature on the addition of Ti4+, Zr4+, and Sn4+ to some Ni‐Zn ferrite compositions are reported and the results are explained on the basis of the movement of the substituting ions first to the tetrahedral and finally to the octahedral sites of the spinel lattice.

Elastic relaxation in transmission electron microscopy of strained‐layer superlattices

Abstract: We demonstrate that thin, cross‐sectioned transmission electron microscopy samples from strained‐layer superlattices undergo elastic relaxation such that the local lattice parameter modulation amplitude can be reduced by a large fraction. Relaxation is dependent on the ratio of the superlattice wavelength to the local sample thickness and is demonstrated experimentally for molecular beam expitaxially grown GexSi1−x superlattices both by selected‐area diffraction and high‐resolution electron microscopy. The results can be qualitatively explained by a simple linear elasticity theory model. Reports of anomalies in the elastic properties of semiconductor superlattices from electron microscopy can be resolved. Evidence is also presented for expected lattice plane bending due to relaxation which can cause strong diffraction contrast. This thin‐sample ‘‘artefact’’ allows unexpectedly weak strain fields to be imaged and permits probing of local elastic properties of individual layers within a superlattice. Simila...

Molecular beam epitaxial growth and transmission electron microscopy studies of thin GaAs/InAs(100) multiple quantum well structures

Abstract: GaAs/InAs(100) multiple interface structures involving 7.4 percent lattice mismatch have been fabricated via molecular beam epitaxy and examined via transmission electron microscopy. It is found that high-quality, dislocation-free interfaces involving such high lattice mismatch can indeed be experimentally realized for very thin layers provided proper care is given to achieve a balance between the growth kinetics and the thermodynamics leading to the equilibrium ground state of the strained layer. The compressive strain is homogeneously accommodated and a tetragonal distortion is induced in the InAs layer with a perpendicular lattice constant in close agreement with that expected on the basis of the continuum theory and elastic constants of bulk InAs.

Theoretical study of solid NaF and NaCl at high pressures and temperatures

Abstract: The static and dynamical properties of NaF and NaCl at high pressures in both the B1 (NaCl) and B2 (CsCl) phases are studied theoretically with an improved electron gas model. The model incorporates the effect of crystal stabilization of the ionic charge densities by way of a Watson sphere-type potential. A series of such calculations as a function of sphere radius is performed to obtain the wave functions of the ions as a function of lattice constant and to obtain the volume dependence of the ion self energy. The latter is shown to make an important contribution to the equation of state. Elastic constants and phonons are calculated in the rigid ion quasi-harmonic approximation. From the effects of compression on the elastic constants and lattice dynamics, mechanical instabilities in both the B1 and B2 phases are identified. The quasi-harmonic frequencies are used to calculate the vibrational free energy and pressure contribution to the equation of state. The calculated (parameter-free) equations of state are found to be in good agreement with the available experimental data for both NaF and NaCl, including the pressure dependence of the thermal expansivity of the B1 phases and recent measurements of the room-temperature compression curves of the B2 phases. The B1–B2 phase transition is examined in detail, and comparisons with experimental and previous theoretical studies are discussed.

Phase constitution and lattice parameter relationships in rapidly solidified (Fe0.65Mn0.35)0.83 Al0.17-xC and Fe3Al-xC pseudo-binary alloys

Abstract: A quasi-equilibrium temperaturevs carbon-concentration phase diagram of rapidly solidified pseudo-binary (Fe0.65Mn0.35)0.83Al0.17-xC alloys was determined after heat treatment in the 823 to 1323 K range. Lattice parameter relationships of rapidly solidified (Fe0.65Mn0.35)0.83Al0.17-xC and Fe3Al-xC alloys in the ferrite, austenite, and perovskite carbide phases were established as a function of the carbon concentration. This study shows that when a high concentration of carbon is present in the alloys a perovskiteL′l2 carbide is formed directly from the rapid solidification process. It is established also in this study that the carbon atom contribution to the lattice parameter increase in the fcc-based cubic crystal is greater in the disorderedγ-phase than in the ordered (L′l2 structure)κ-phase.