Zur Heteroepitaxie von AIBIIIC2VI-Verbindungen – Interpretation von RHEED-Diagrammen

Semiconductors of the A^IB^IIIC₂^VI type, crystallizing in the chalcopyrite structure, grow epitaxially with their {112}-planes on monocrystalline substrates with a three-fold symmetry of faces. It is shown that application of the RHEED technique permits definitively to decide what kind of epitaxial overgrowth takes place, supposing the atomic scattering factors of the I and III atoms are sufficiently different and/or the c/a axis ratio differs markedly from 2. CuInSe₂/GaAs and CuGaSe₂/GaAs show one-dimensional epitaxy     

Determination of lattice parameters at thin epitaxial layers by RHEED

A simple method is described for measurement of lattice parameters of thin heteroepitaxial layers by RHEED technique using the substrate as a calibration substance. Results are presented for special cases of I–III–VI₂ chalcopyrite type semiconductor epilayers on GaAs substrates. The accuracy of the method is in the order of about 5 · 10⁻³.     

Microhardness-Plasmon Energy-Bulk Modulus Relationship in Ternary Chalcopyrite Semiconductors

In this paper simple relations have been proposed for the calculation of microhardness and bulk modulus of I–III–VI₂, and II–IV–V₂, chalcopyrite semiconductors. The present calculations do not require any experimental data except the plasmon energy of the semiconductors. A linear relation between bulk modulus and microhardness has also been obtained. Our calculated values are in fair agreement with the experimental values and the values reported by different workers.     

Structure types – a review

Structures of binary inorganic A_xB_y compounds with A and B on two Wyckoff positions are characterized by the self‐coordination numbers T_i, i = 1–3, of A and B atoms. The T₁ = 0–12 values of 122 structure types can be correlated with different topologies, A–A interactions and densities. High T₁ values like T₁ = 12 are obtained for fcc or hcp sphere packing with maximum density of A atoms and interstitial B atoms. Hexagonal or tetragonal layered compounds are recognized by the T_i values 6 6 6 or 4 4 4. The T₁ = 2 values are found for chains, T₁= 1 for ordered molecules like N₂ or Br₂. The A and B atoms of few compounds like NaCl or CsCl form a pc or bcc sphere packing. The T₁ = 0 values of Na or Cs atoms indicate repulsive Na–Na or Cs–Cs interactions. Distorted structures of a structure type are recognized, if atoms with slightly different A–A or B–B distances are included in the proper coordination shells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bestimmung der relativen Stabilität der Zinkblende- und Wurtzitstruktur mit Hilfe des piezoelektrischen Effektes

A phenomenological model of the piezoelectric effect is used to determine the relative stability of zineblende and wurtzite structure in A_II B_VI-semiconductors. It is shown that compounds with a normalized longitudinal piezoelectric constant e_pol* > 0,15 ± 0,02 are stable in wurtzite but compounds with e*_pol < 0,15 ± 0,02 are stable in zineblende structure.     

The Ln–Ba–Cu–O (Ln = Lanthanoid) systems: Compounds and compatibilities in air at 900–980°C

Comparison of phases observed in air at 900–980°C in the Ln–Ba–Cu–O (Ln = Lanthanoid) systems is reported. On the basis of the occurrence of compounds found in these Ln₂O₃–BaCO₃–CuO systems they must be divided into at least three subgroups: the first is characteristic of La, Pr and Nd, the second specific for Sm and Eu, and the third common to the smaller lanthanoids, the Y-type elements, with some variation within the groups.     

Comparative infrared lattice vibration study of LiGaO2 and LiInO2 (II). Interatomic force constants

The frequencies of the wurtzite-like modes due to Li–O and Ga–O bond vibrations in LiGaO₂ and of the rocksalt-like mode due to Li–O bond vibrations in LiInO₂ are determined from the infrared reflectivity spectra of the compounds. The force constants for the Li–O and Ga–O bonds in LiGaO₂ follow the same trends as those found for the A^IB^IIIC₂^VI chalcogenides with tetrahedral cordination. The results for LiInO₂ are compared with measurements on the octahedrally coordinated modification of LiAlO₂.     

A study of a fast ionic conductor–Ag1−xCuxI

The Conductivity of AgI–CuI system has been studied. Two molar ratios of the system Ag_1–xCu_xI with x = 0.05 and 0.15 have been taken. The transition temperatures are observed with conductivity measurements.     

Heat capacity of LiInS2, LiInSe2 and LiInTe2 between 200 and 550 K

The molar heat capacity at constant pressure of LiInS₂, LiInSe₂ and LiInTe₂ was measured in the temperature range from about 200 K to 550 K. An analysis of the experimental data showed that the anharmonic contribution to the heat capacity can be described by a polynomial of fourth order in the temperature. A comparison of the results for the LiInC₂^VI compounds with those for the AgB^IIIC₂^VI and A^IIB^IVC₂^V chalcopyrite compounds showed that the lattice anharmonicity effects are essentially influenced by the specific nature of the Li C^VI bond.     

Processes of vapor phase growth of AIIBVI single crystals and structures based there upon

Results of investigations of semiconductor A^IIB^VI compounds (for example of CdTe and ZnTe) grown by the chemical vapor transport (CVT) method in a closed volume using three transfer agents containing a halogen, compound NH₄X (X = Cl, Br, I) are presented. The processes of vapor phase growth (composition of the vapor phase and mass transfer) in Me(Cd, Zn)Te–NH₄X (X = Cl, Br, I) systems have been calculated theoretically and the results are have been verified in growth experiments. Optoelectronic properties of the grown materials and barrier structures based there upon are discussed.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (I) Keating Model Considerations

The lattice vibrations of the A^IIB^III₂C^VI₄ semiconductors with defect-chalcopyrite structure are treated in a simplified version of the Keating model considering only interaction with nearest neighbours and assuming that all anions occupy their ideal lattice sites. It is found that in this model the frequencies of the nonpolar and polar modes with highest energy are determined by the properties of the B^III–C^VI sublattice alone. The frequencies of all the other optical modes depend not only on the A^II–C^VI and B^III–C^VI interactions but are also influenced by the presence of the ordered array of vacancies. The results obtained are compared with previous model considerations.     

Über die röntgenographische Analyse der mittleren quadratischen Atomverschiebungen in einigen Halbleiterkristallen

X-ray measurements of the Debye-Waller factor were performed with single crystals of Ge and of semiconducting compounds A^IIIB^V, A^IIB^VI, A^IVB^VI in the temperature range 100 K — 1000 K. From the results the mean square atomic displacements 〈u²〉 and the Debye characteristic temperatures θ of the materials were calculated. Both parameters are discussed with respect to the influence of the temperature, the influence of point defects and, in the case of the compounds, deviations from the stoichiometric composition on the thermal lattice vibrations. Finally, considerations are presented, concerning the relationship between the parameters 〈u²〉 and θ_M, respectively, and the activation energies of vacancy formation and diffusion in the materials.     

Investigation of GaAs—InyGa1−yPzAs1−z–InxGa1−x-As grading heterojunctions formation

The initial stages of growth of GaAs–InGaAsP_var–In_xGa_1−xAs heterostructures (x = 0.1 and 0.17) were investigated for the equilibrium-cooling method of LPE growth. Similar investigations were carried out for GaAs–InGaAsP_var–In_0.05Ga_0.95As heterocompositions, but for the step-cooling technique. The scheme of growing of In_0.17Ga_0.83As films of GaAs substrates with several intermediate buffler InGaAsP_var layers is represented. These heterostructures were shown to have less than 10⁶ cm⁻² dislocation density on the overall area of the film (> 2 cm²).     

Calculation of the atomic scattering factors of fast electrons at zero angle of incidence of an electron beam and mean inner crystal potentials

The atomic scattering factors of fast electrons at zero angle of incidence of an electron beam, f _el(0), are calculated for neutral atoms with Z = 1?54, using the mean-square radii of electron-density distributions in atoms and ions, derived on the basis of the Hartree-Fock wave functions. The values of f _el(0) have been calculated for the first time for some positive and negative ions. The obtained values of f _el(0) were used to determine the mean inner potentials V₀ of metallic, covalent, and ionic crystals. The calculated values of V₀ are compared with the experimental data in the literature. The values of V₀ calculated for III–V and II–VI compounds are reported.     

Bond Ionicities and Structural Trends in Some LiBIIIC Compounds

The individual and average bond ionicities of LiAlO₂, LiGaO₂, LiInS₂, LiInSe₂ and LiInTe₂ are evaluated from spectroscopic data. It is found that in these compounds the Li C^VI bond is essentially ionic in nature. It is shown that the structural properties of the compounds can be understood in terms of the average bond parameters.     

An X-ray diffraction study of mesoionic 1-thia-2,3,4-triazolo-5-aminidine and some of its derivatives

X-ray diffraction data are presented for the title mesoionic compound (I), its hydrochloride salt (II) and methylated derivative (III). The crystal of (I) is orthorombic, space group P2₁2₁2₁, with cell dimensions: a = 5.857(1) Å, b = 12.494(2) Å, c = 16.328(3) Å, with four molecules per unit cell. The crystal of (II) is monoclinic, space group P2₁/n, with cell dimensions: a = 5.5720(10) Å, b = 21.5770(4) Å, c = 11.2330(2) Å, beta = 95.15(3)°, with four molecules per unit cell. The crystal of (III) is monoclinic, space group P2₁/n, with cell dimensions: a = 12.0886(5) Å, b = 7.9103(4), c = 104.29(1) Å, beta = 104.29(1)°, with four molecules per unit cell. Of particular interest is the fact that the C5–N6 bond appears to have a high double bond character in all three of the compounds studied. In addition, it is found that the exocyclic N-phenyl group changes from being in the cis conformation with respect to sulfur in compounds (I) and (III) to the trans conformation in the hydrochloric salt (II).     

T(x) phase diagram of the CuSbS2–CuInS2 system and solubility limit of Sb in CuInS2

The starting ternary compounds CuInS₂ and CuSbS₂ and alloys of the CuSbS₂–CuInS₂ system with the molar fractions of CuInS₂ (x) equal to 0.05, 0.15, 0.25, 0.375, 0.50, 0.625, 0.75, 0.85, and 0.95 were prepared and the phase relations in this system were investigated by X‐ray powder diffraction, optical microscopy, scanning electron microscopy, and differential thermal analysis. It was shown that the T–x phase diagram of the CuInS₂–CuSbS₂ system has a eutectic character with the eutectic temperature of 807 K. The alloys of the CuSbS₂–CuInS₂ system with the molar fraction of CuInS₂ in the range from 0.038 to 0.941 at room temperature are two‐phased, and the limits of solubility are 0.059 molar fractions for CuSbS₂ in CuInS₂ and 0.038 molar fractions for CuInS₂ in CuSbS₂.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (II). Analysis of Nonpolar Optical Modes

A simplified version of the Keating model originally derived for defect-chalcopyrite compounds is extended to include all A^IIB₂^IIIC₄^VI compounds with ordered arrays of vacancies. It is shown that the trends and frequencies of the nonpolar optical modes of these compounds can be described within this model. Simple scaling laws for the interatomic force constants are proposed and compared with corresponding relations for other binary and ternary compounds with tetrahedral coordination.     

The structure of tetrahedrally coordinated amorphous semiconductors

The diffracted X-ray intensities, F(k)'s, and radial distribution functions of Ge, some III–V compounds, and Ge_0.5Sn_0.5 are presented. It is shown that the radial distribution functions of the III–V compounds are similar to those of Ge. If the continuous random network, as developed for amorphous Ge, is also applicable to the III–V's, then several bonds between like atoms (wrong bonds) must be present. It is argued that the energy of wrong bonds may not be sufficiently high to prohibit their formation.     

Crystal structures of X‐phase in the Sb–Te binary alloy system

It is well known that the Sb–Te binary system has a large number of incommensurately or commensurately modulated structures between Sb and Sb₂Te₃ compounds. These structures, which are long‐period trigonal stacking structures, possess their own modulation period γ, according to their composition in the thermal equilibrium. However, the structure of sputtered Sb–Te films with various compositions between the two compounds at both ends formed in a non‐thermal equilibrium showed smaller γ values, than those expected from their compositions without exception. A smaller γ value implies that its structure is closer to that of Sb with the shortest period in all Sb–Te modulated structures. With increase in temperature, all these transient structures with smaller γ, however, became stable, accompanying an increase of γ to acquire their original modulated structures.