Ionicity of the chemical bond in AIBIIIC semiconductors

The Phillips — van Vechten dielectric theory for binary tetrahedral compounds and Levine's extension of this theory to multibond crystals is used to evaluate the bond ionicities in the A^IB^IIIC chalcopyrite compounds with A^I = Cu, Ag from spectroscopic data. In deriving the ionicity of the A^I—C^VI bond the influence of the noble metal d electrons it taken into account. The results obtained are compared with previous estimations.     

Thermal expansion anisotropy and individual bond expansion coefficients in ternary chalcopyrite compounds

The individual bond expansion coefficients of the A^IIB^IVC and A^IB^IIIC₂^VI chalcopyrite compounds are calculated from the principal linear thermal expansion coefficients of the lattice parameters using the regular B C tetrahedron model and a model with a temperature independent free parameter of the lattice. It is shown that the bond expansion coefficients derived from the latter model are in better agreement with the trends found for the interatomic forces in the chalcopyrite compounds and observed for the thermal expansion coefficients in the binary AC, A^IIC and BC compounds.     

Trends in the microhardness of the CuBIIIC chalcopyrite compounds

On the basis of a microhardness scaling law found for the A^IIB^IVC compounds and of the dependence of the microhardness on conductivity type and composition observed experimentally in CuInSe₂ a model is proposed to describe the trends in the microhardness of the CuB^IIIC compounds. The results are compared with experimental data and other microhardness estimates. It is found that most of the existing microhardness measurements can be interpreted within the model.     

Spectroscopic analysis of the heat of formation in AIBIIIC compounds

The spectroscopic model for the heat of formation of tetrahedrally coordinated binary compounds is extended to the ternary chalcopyrite semiconductors. The heats of formation of all A^IB^IIIC compounds are evaluated and compared with experimental data. Possible reasons for existing discrepancies between theory and experiment are discussed.     

Force constant scaling and interatomic potential in tetrahedral semiconductors

The force constants of tetrahedral semiconductors derived from lattice vibration data are analysed in terms of a generalized Morse potential and of a potential with power laws of the interatomic distance for the repulsive and attractive term. It is found that the Morse potential is an appropriate model for describing the dependence of the force constants on the bond length in the elemental, A^IIIB^V, A^IIB^VI and A^IB^IIIC semiconductors.     

Epitaxy of AIBIIIC semiconductors

Epitaxial layers of A^IB^IIIC compounds were grown by the flash evaporation technique and investigated using reflection electron diffraction. Geometric-structural considerations allow the prediction of epitaxial relationships and types of epitaxy (one- or three-dimensional, multiple orientation). These properties of the epitaxial layers were confirmed experimentally. Furthermore, the epitaxial temperature ranges, non-equilibrium phases, defects, and special features of the epitaxial growth are described. Especially, the influence of lattice misfit is discussed.     

Heat capacity and lattice anharmonicity in CdBIVC chalcopyrite compounds

The heat capacity at constant pressure of CdSiP₂, CdGeP₂, CdSnP₂ and CdGeAs₂ is measured in the temperature range from 300 to 500 K. The anharmonic contribution to the heat capacity is evaluated and it is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds. Comparing the temperature variation of the heat capacity and of the thermal expansion coefficient some conclusions are made regarding the interatomic potential in the A^IIB^IVC compounds.     

Surface preparation of AB semiconductors (Cd3As2, Zn3As2, Cd3P2, Zn3P2) under ultra-high vacuum conditions

The UHV surface preparation of AB materials (crystals and thin films) has been monitored with XPS and AES. Clean and stoichiometric surfaces of AB crystals were prepared by means of low energy ion bombardment and subsequent low temperature annealing. Stoichiometric Cd₃As₂ and Zn₃P₂ thin films with very low amounts of C and O were deposited by the evaporation of bulk material in the UHV. The quality of prepared AB crystal and thin film surfaces was sufficient to carry out density of states investigations (UPS, RELS) with success.     

Microhardness scaling and bulk modulus-microhardness relationship in AIIBIVC chalcopyrite compounds

An analysis of experimental microhardness data shows that the microhardness of the A^IIB^IVC compounds can be described by a simple scaling law which depends only on the unit cell volume and the melting temperature. On the basis of this result a simple bulk modulus — microhardness relationship is proposed and used to estimate the bulk moduli of the compounds. The results are compared with existing literature data.     

Defect studies in CuBIIIC chalcopyrite compounds using the ion channeling technique

Based on simple approximations the backscattering minimum yield is estimated for axial ion channeling in perfect crystals of six CuB^IIIC chalcopyrite compounds. The results obtained for CuInSe₂ are compared with experimental channeling spectra. Point defect concentrations up to about 10²¹ cm⁻³ are estimated for CuInSe₂ single crystals grown by the vertical Bridgman method. A simple power law is found for the fluence dependence of the damage density in oxygen implanted CuInSe₂ single crystals.     

Absorption and ionic conductivity of oxygen-containing SrF2 crystals

An absorption band at 3644 cm⁻¹ is caused by isolated OH⁻ ions. O⁻ ions cause an absorption band at 213 nm the oscillator strength of which is 0.020. Charge-compensation of O⁻ ions is effected by F⁻ ion vacancies (F). As for CaF₂ crystals there occur monomers and dimers of [O⁻ – F] complexes. The mass action constants of association of F with oxygen centres are K_AD = ⅓ exp (4.28 – 0.82 eV/kT) for [O⁻ – F], K_AT = 4 exp (17.4 – 1.25 eV/kT) for [2 O⁻ – F] and K_AQ = exp (4.2 – 0.89 eV/kT) for [2 O⁻ – 2 F].     

Hyperfine structure of Cr5+ EPR spectra in X-irradiated potassium halide crystals doped with CrO and Ca2+

The hyperfine structure has been investigated in the EPR spectra of X-irradiated KCl: CrO, Ca²⁺ and KBr: CrO, Ca²⁺ crystals. Preliminarily spectra were simplified by means of heating the crystals up to 400 K for KCl and 440 K for KBr, that destroys the less stable CrO · V centers. It is ascertained, that principal directions of g- and A-tensors do not coincide, and principal A-values are determined. Calculations, making use of the experimental meanings of g- and A-tensor components, showed, that the degree of distortion of oxygen tetrahedra in CrO · Ca²⁺ · V centers is almost the same in both KCl and KBr crystals; besides, these calculations suggest the existence of a strong covalent bonding between the central Cr⁵⁺ ion and four oxygen ligands in CrO ions.     

Interatomic force constants in AIIBIVCV2 chalcopyrite compounds

Force constants of the A^II C^V and B^IV C^V bonds in the A^IIB^IVC^V₂ compounds with chalcopyrite structure are estimated from experimental lattice vibration data using a simplified version of the Keating model. It is shown that the force constants depend exponentially on the bond length. The parameters of this relation are practically the same as those found for the A^IV A^IV, A^III B^V and A^II B^VI bonds in the elemental semiconductors and binary compounds and for the B^III C^VI bond in the A^IB^IIIC^VI₂ semiconductors.     

Magnetic and electric properties of the ternary alloys AB

The results of experimental studies of the electrophysical and magnetic properties of solid solutions based on the AB compounds with anion (Zn₃(P_xAs_1−x)₂ and cation (Zn_xCd_1−x)₃ P₂ substitution are reported. The Zn₃(As_xP_1−x)₂ solid solutions are characterized by p-type conductivity (∼ 10¹⁵  10¹⁷ cm⁻³), low Hall mobility and conductivity of ∼ 10⁻² — 10⁻³ ohm⁻¹ cm⁻¹. In the (Zn_xCd_1−x)₃P₂ solid solutions the samples rich in zinc are p-type, those rich in cadmium — n-type, the carrier concentration is ∼ 10¹⁶ — 10¹⁸ cm⁻³. From the measurements of the magnetic properties of the above mentioned alloys it is shown that in the investigated solid solutions a transition from the structure with direct optical transition to those with indirect optical transition occurs.     

On the mechanism of chemical polishing of GaAs crystals

In order to establish reproducible conditions for chemical lap polishing of GaAs with NaOCl solutions, containing also OH⁻- and CO -ions, the mechanism of dissolution was investigated using the rotating disk arrangement. In solutions with excess OCl⁻ concentrations likewise diffusion and a reaction of the first order with respect to OH⁻ and CO, complexing agents for Ga-ions, control the dissolution rate, and the surfaces of the wafers are polished. OH⁻ and CO₃^2– concentrations in excess with respect to OCl⁻ lead to rate determining OCl⁻ diffusion and to irregularly polished or film covered surfaces. Diffusion constants for OH⁻, CO and OCl⁻ are given.     

Investigations on electronically conducting oxide systems (XI) electrical conductivity and optical absorption of a -and c-Domain crystals BaVTiO3

BaVTiO₃ single crystals can be grown from a basic BaCl₂ flux. The electric conductivity was measured at a- and c-domain crystals and optical absorption as well as photoconductivity were ascertained at a-domain crystals using plane polarized light in dependence on direction. Properties and their anisotropy are discussed on the basis of their local relations in the ferroelectric host lattice and compared with the properties of BaNbTiTiO₃ single crystals described in the preceding communication.     

Density and mobility of anti-frenkel defects in SrF2 crystals

By fitting the theoretically calculated temperature-dependent conductivity σ to the measured dependencies log σT ÷ 1/T the following parameters have been determined: free formation enthalpy of anti-Frenkel defects g_AF = 2.05 eV – 6.35 kT; mobilities of F⁻ion vacancies F and interstitials F: v_νT = 600 exp (-0.70 eV/kT) cm² K/Vs, v_iT = 1.1 · 10⁴ exp (-0.93 eV/kT) cm² K/Vs. — The free association enthalpies of complexes consisting of single foreign ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, Li⁺, K⁺, Na⁺, O⁻) and the charge-compensating defect were obtained. The vibration frequency of F⁻ ions in the neighbourhood of F and F is changed by a factor of 2.6 and 0.6, respectively.     

Strukturelle Umklapp-Vorgänge in metastabilen β1-Kupfer-Zink-Mischkristallen bei tiefen und höheren Temperaturen (I). Gitterdynamische Skizze1)

The quantity of the shear-modulus G′ = (c₁₁ – c₁₂)/2 is a measure for the probability of structural Umklapp-processes to occur in metastable β₁-Cu-Zn-solid solutions. Such processes take place, if G′ = G′(T, x) would fall below a critical limit, G′_crit, e.g. by lowering of temperature T or/and Zn-concentration x, because the Fermi-contribution to G′will sink in the 1^st and with him additional the Coulomb-contribution in te 2^nd case. Both ones are the authoritative stabilizing factors for β₁ and therefore specific fo its lattice-dynamical behaviour, especially in the longwavy range of thermoacoustic lattice-vibrations, by which the cooperative Umklapp-motion will escape. Umklapping can also be initiated by favourably oriented dislocations, is G′ would approach to G′_crit in their neighbourhood: G′_critG′(xM8), with xM8  Umklapp-concentration. This is possible by variation of x during isothermal reactions, in the course of whicht he β₁-matrix will heterogenize itself into Zn-poorer and -richer districts β and β (pre-diffusion by means of quenchy vacancies). Both kinds of districts, among which the latter ones will enhance their degree of stability, are joint together coherently. They build up a so called β /β -parquet. The parquet-bricks can reach a critical size, which is necessary that sufficient large atom-collectives can simultaneously be caused to an Umklapp-motion and to occupate new equilibrium positions by thermo-acoustic shear-waves (comparison with a sin-wave beeing changed to a zigzag-line). Only at higher temperatures the bricks come up to the critical size. Umklapping comes about only in the β -bricks, which turn by it to a transition lattice (β₂) with a structure similary to that of the lowtemperature-martensite β′′. After that β₂ changes to α-phase. The way β ⇒ α is marked by the following steps: prediffusion, Umklapping + dislocation, leading to β₂, and a further dislocation dissoziation, leading the atoms to the equilibrium positions in the α-lattice. The so stepped mechanism acts an nucleationmechanism of the α-phase. After the nucleation the α-nuclei grow at the cost of too much formed β (postdiffusion). By isothermal reactions at too low temperatures a mini-herterogenized state of the β₁-matrix will be caused comparable with coldhardening states of other alloys (Guinier-Preston-zones). A β₁-matrix in such a state is unable to isothermal Umklapping, so that α-crystals can be formed – provided that the mini-heterogenities are resolved by increasing of the reaction temperature.     

Lattice Thermal Expansion in CuGaT2 and CuInTe2 Compounds over the Temperature Range 80 to 650 K from X-ray Diffracion Data

The lattice parameters a and c as well as the thermal expansion coefficients α⟂ and α∥ in the two principal direction for CuGaTe2 and CuInTe 2 chalcopyrite-type compounds have been determined as a function of temperature in the range from 80 to 650 K by the X-ray diffraction method. It is found for both the compounds the coefficient of expansion along the α axis (α⟂) is larger than that along the c axis (α∥) over the whole investigated tem-perature range. When comparing the results for a series of the CuB^IIIC compounds (B Ga, In; C S, Se, Te) it is shown that the thermal expansion anisotropy increases strongly when the Ga atom replaces the In atom while it changes a little when the Te atom replaces the Se atom or the S atom.     

The influence of the direct quench and indirect quench to Ta > Th on the decomposition behaviour of an Al-2 at.% Zn-1 at.% Mg alloy

The decomposition behaviour of an Al-2.0 at.% Zn-1.0 at.% Mg alloy after direct quench (DQ) and indirect quench (IQ:T = 23 °C, t) to the ageing temperature T = 160 °C (above the temperature of the rapid homogeneous nucleation, T_h) was investigated by means of TEM and isothermal resistivity measurements. The precipitation density of the η-particles yields a maximum value at pre-ageing times about 10 min at T = 23 °C. To clear up the reason for that phenomenon a loop-formation and clustering model was introduced.