Showing papers in "Crystal Research and Technology in 1989"

On the preparation and electrical properties of thallium selenide monocrystals

Abstract: Thallium Selenide single crystals were prepared by a special design using Bridgmantechnique constructed by the authors. An investigation was made on the influence of temperature on the electrical conductivity and Hall effect in two crystallographic directions. The anisotropic properties were checked, and the anisotropic factor was observed to increase with temperature decrease. The energy gap as well as the ionization energy was calculated. The conductivity throughout the entire temperature range was found to be of p-type. The Hall mobilities derived from these measurements at room temperature were of the order μH⟂ = 42.66 cm2/vs and μH∥ = 112.2 cm2/vs.

Growth rate dispersion — a review

Abstract: The growth rate dispersion (GRD) is reviewed from its start up to today. A definition is given followed by a summary of the facts and the first approaches for explanations. This all are surface reaction steps. The discussion of the consequences – no size dependent growth – is carried through. At the end the models (RF-and CCG-model) will be introduced which make it possible to work with the growth rate dispersion instead of size dependent growth. The newest approach is the superpositioning of the two models, this is perhaps the most promising way. Die Growth Rate Dispersion (GRD) wird betrachtet von ihrer ersten Erwahnung bis heute. Uber eine Definition und eine Bestandsaufnahme fuhrt der Weg zu den Erklarungsansatzen. Es handelt sich um Oberflacheneffekte. Die Diskussion der Folgen – kein grosenabhangiges Wachstum – wird durchgespielt. Am Ende werden die Modellvorstellungen (RF- und CCG-Modell) vorgestellt, die es ermoglichen mit der Growth Rate Dispersion anstelle von grosenabhangigem Wachstum zu arbeiten. Es wird auch deutlich gemacht, das eine Uberlagerung dieser Modelle der neueste und erfolgversprechendste Weg zu sein scheint.

Crystal growth and dislocation structure of gallium antimonide

Abstract: Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 102 cm−2.

Rietveld refinement of Y2O3 using the Pearson VII profile shape function

Abstract: Very good agreement between the observed and the calculated intensities was obtained using the Pearson VII profile shape function. The variable exponent m could be refined only in the damped iterations involving exclusively the profile parameters. Simultaneous refinement of the m with the positional and/or thermal parameters has led to large oscillations of the shifts of almost all parameters. Precision of the refined atomic coordinates is better than those from previously published Rietveld refinement and is comparable with single crystal results. The degree of serial correlation in residuals has been determined by the use of the Durbin-Watson d statistic. Normal probability plot based on δRi has been almost linear with the slope greater than one. The weighting scheme with wi = 1/yoi has proved to be good first approximation.

Electrooptical coefficients and temperature and pressure derivatives of the elastic constants of tetragonal Li2B4O7

Abstract: New values for the following properties of tetragonal Li 2 B 4 O 7 are reported: dielectric, electrostrictive, electrooptic, elastic, thermoelastic and piezoelastic constants, coefficients of thermal expansion and indices of refraction. These values are considered to be of superior precision compared to earlier published data

Electrooptic properties of polycrystalline SnSe thin films

Abstract: It is observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature. The study of variation in band gap with thickness shows a linear relationship between band gap and 1/t2. Finally, band gap – substrate temperature studies show that the band gap increases with substrate temperature.

Interatomic force constants in AIIBIVCV2 chalcopyrite compounds

Abstract: Force constants of the AIICV and BIVCV bonds in the AIIBIVCV2 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 AIVAIV, AIIIBV and AIIBVI bonds in the elemental semiconductors and binary compounds and for the BIIICVI bond in the AIBIIICVI2 semiconductors. Kraftkonstanten fur die AIICV- und BIVCV-Bindungen in den AIIBIVCV2-Verbindungen mit Chalkopyritstruktur werden aus experimentellen Gitterschwingungsdaten unter Verwendung einer vereinfachten Version des Keating-Modells abgeschatzt. Es zeigt sich, das die Kraftkonstanten exponentiell von der Bindungslange abhangen. Die Parameter dieser Beziehung haben praktisch dieselben Werte wie im Falle der AIVAIV-, AIII-BV und AIIBVI-Bindungen in den Elementhalbleitern und binaren Verbindungen und der BIIICVI-Bindung in den AIBIIICVI2-Halbleitern.

Estimation of point defect parameters of solids on the basis of a defect formation model of melting (II). Vacancy formation enthalpy in relation to the heat of fusion and the increase of volume due to melting

Abstract: The mole fraction of vacancies within melts at their melting points is found to be xL = = 0.125 in the case of elements (with exception of inert gases), alkali halides, binary oxides and organic compounds. As to inert gases it is xL = 0.194. The formation enthalpy of vacancies (Schottky defects) is given by hS = L/xL (L heat of fusion) in every case. The increase of volume due to melting can be explained well by the vacancy model of melting: ΔV = VSxL (VS formation volume of Schottky defects). In Schmelzen ist am Schmelzpunkt der Molenbruch der Leerstellen xL = 0,125 bei Elementen (ohne Edelgase), Alkalihalogeniden, binaren Oxiden und organischen Verbindungen. Bei Inertgasen ist xL = 0,194. Die Bildungsenthalpie der Leerstellen (Schottky-Defekte) ist in jedem Fall hS = L/xL (L Schmelzwarme). Die Volumenzunahme ΔV beim Schmelzen kann gut durch das Leerstellenmodell des Schmelzens erklart werden: ΔV = = VSxL (VS Bildungsvolumen der Schottky-Defekte).

Force constant scaling and interatomic potential in tetrahedral semiconductors

Abstract: 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, AIIIBV, AIIBVI and AIBIIIC semiconductors. Die Kraftkonstanten tetraedrischer Halbleiter, die aus Gitterschwingungsdaten bestimmt wurden, werden im Rahmen eines verallgemeinerten Morsepotentials und eines Potentials mit Potenzgesetzen des zwischenatomaren Abstands fur den abstosenden und anziehenden Term analysiert. Es zeigt sich, das das Morsepotential ein geeignetes Modell fur die Beschreibung der Abhangigkeit der Kraftkonstanten von der Bindungslange in den Elementhalbleitern sowie den AIIIBV-, AIIBVI- und AIBIIIC- Verbindungen darstellt.

Formation of α-Al2O3 by thermal decomposition of basic aluminium chlorides at low temperatures

Abstract: Basic aluminium chloride gels and the crystalline salt AlCl3 · 2 Al(OH)3 · 6 H2O are thermally decomposed to an amorphous product in a first step at low temperatures. If the reaction gas is rapidly removed the amorphous decomposition product directly transforms to corundum at increased temperature. Starting from gels the α-Al2O3 formation begins at 420 °C, transformation of the crystalline salt at 530 °C. Structural similarities of precursor compounds and corundum are discussed as a reason for this behaviour. High contents of HCl and H2O in the atmosphere surrounding the specimen result in decomposition to transition aluminas at increasing temperature, which are transformed into α-Al2O3 above 1000 °C.

Estimation of point defect parameters of solids on the basis of a defect formation model of melting (I)

Abstract: It is proposed that the melting process is governed by the creation of lattice defects followed by a relaxation of the lattice in the vicinity of the defects. At the melting point Tm the mole fraction xL of defects within the melt is given by xL = L/ho (L heat of fusion; ho formation enthalpy of defects within the solid). Es wird vorgeschlagen, das der Schmelzprozes durch die Erzeugung von Gitterdefekten mit nachfolgender Relaxation des Kristallgitters in der Nahe der Defekte bestimmt wird. Am Schmelzpunkt Tm ist der Molenbruch xL der Defekte in der Schmelze gegeben durch xL = L/ho (L Schmelzwarme; ho Bildungsenthalpie der Defekte im Festkorper).

Temperature dependences of the electrical conductivity and hall coefficient of indium telluride single crystals

Abstract: Conductivity type, carrier concentration and carrier mobility of InTe samples grown by Bridgmann technique were determined by the Hall effect and electrical conductivity measurements. The study was performed in the temperature range 150–480 K. Two samples with different growth rate were used in the investigation. The samples under test were P-type conducting, in accordance with previous measurements of undoped material. The Hall coefficient was found to be isotropic yielding room temperature hole concentration in the range 1015 – 1016 cm−3. The hole mobilities of InTe samples were in the range 1.17 × 103 – 2.06 × 103 cm2/V · sec at room temperature. The band – gap of InTe determined from Hall coefficient studies has been obtained equal to 0.34 ev. The scattering mechanism was checked, and the electrical properties were found to be sensitive to the crystal growth rate.

Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts

Abstract: Electrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n-GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm2/V · sat n = 2.5 · 1014 cm−3 has been grown). [Russian Text Ignored].

Isomorphic substitutions in the CeO2La2O3 system at 850° C

Abstract: It was proved that there are two isomorphic series of mixed crystals in the CeO2La2O3 systems from 0 to 14 mol% CeO2-mixed crystals based on the La2O3 structure and from 32 to 100 mol% CeO2-mixed crystals based on the CeO2 structure. The oxides were obtained by co-precipitation of oxalates, followed by heating at 850 °C. The changes of the parameters of the lattice with the changes of the composition were investigated. Also the solubility of the mixed crystals in 25% HCl was determined. [Russian Text Ignored].

The development of a nematic two frequency addressing mixture

Abstract: An example is given for the development of a nematic two frequency addressing mixture based on the equations for the threshold voltages, the switching times, and the dielectric relaxation. New substances have been synthesized with relaxation frequencies in the kHz range and big values of the static dielectric anisotropy at room temperature. The isotropy frequency and the relation between the high and low frequency dielectric anisotropy, respectively, are adjustable by adding of substances without a relaxation mechanism in the kHz range and with a big negative static dielectric anisotropy. The produced mixture was dielectrically investigated. Calculated and experimentally found data are in a good agreement. Es wird ein Beispiel gegeben fur die Entwicklung einer nematischen Zweifrequenz-adressierbaren Mischung auf der Grundlage der Gleichungen der Schwellspannungen, der Schaltzeiten und der dielektrischen Relaxation. Neue Substanzen wurden synthetisiert mit Relaxationsfrequenzen im kHz-Bereich und grosen statischen dielektrischen Anisotropien bei Raumtemperatur. Die Isotropiefrequenz und damit das Verhaltnis zwischen der statischen und der hochfrequenten dielektrischen Anisotropie kann durch Zugabe von Substanzen, die grose negative statische dielektrische Anisotropien besitzen und keinen Relaxationsmechanismus im kHz-Bereich zeigen, eingestellt werden. Die von uns hergestellte Mischung wurde dielektrisch untersucht. Die berechneten und die experimentell ermittelten Daten stimmen gut uberein.

Structure and properties of Na-magadiite dependent on temperature

Abstract: The mechanism of the thermal behaviour of Na-magadiite at a temperature range from 293–573 K was developed based on X-ray diffraction, DTA, DTL, Q-TG, and gravimetric measurements. A structure model (BRANDT et al.) previously proposed was additionally used. It is possible to show that there probably is a connection between the typical modifications of basal spacing and significant shiftings of silicate sheets. Different steps of dehydration, decrystallization and structure variations can be ascribed to the several thermal transitions. The results depend on sample treatment such as the existent or not existent solid-water vapour interaction and the establishment of equilibrium. It seems that there is a predominance of the first mentioned influence. Das thermische Verhalten des Na-Magadiites wird mit Rontgenpulvermessungen, DTA, DTL, Q-TG und gravimetrischen Messungen charakterisiert. Die Ergebnisse sind abhangig vom Gang der Messung (kontinuierlich, diskontinuierlich) und von der Probenhalterung (luftoffen, geschlossen). Unter Einbeziehung eines bereits fruher entwickelten Struktur-modells (BRANDT et al.) ist es moglich, konkrete Vorstellungen uber Strukturveranderungen bei den verschiedenen thermischen Umwandlungen zu entwickeln. Es last sich zeigen, das sprunghafte Veranderungen des Basalabstandes signifikanten Verschiebungen der Modellsilikatschichten gegeneinander entsprechen.

Density studies across smectic‐smectic transitions in 70.6 and 80.10

Abstract: The temperature dependence of density in N(p-n-heptyloxy benzylidene) p-n-hexylaniline (70.6) and in N(p-n-octyloxy benezylidene) p-n-decylaniline (80.10) is carried out to study the nature of the phase transitions associated density jumps, to estimate the pressure dependence of transition temperatures and pretransitional effects. The compounds 70.6 exhibits a phase variant ACFG whereas 80.10 exhibits a new phase sequence variant ABF. The isotropic-smectic A, semctic A-smectic B and semctic C-smectic F phase transitions are found to be first order. The calculated thermal expansion coefficient also supported the density results. The density jumps, associated enthalpies and estimated pressure dependence of transition temperatures at the isotropic-smectic A phase transformation in other compounds are presented.

Vickers indentation hardness of Hg1−xCdxTe

Abstract: The Vickers indentation hardness of Hg1−xCdxTe has been measured as a function of composition x using monocrystalline samples of Bridgman and THM crystals and polycrystalline starting material at room temperature. The microhardness varied between 220 MPa (x=0) and 440 MPa (x=1), showing a maximum of 850 MPa at x ∼ 0.75, and was different between monocrystalline and polycrystalline samples. The “hardening rate” dH/dx is strongly dependent on the composition range and is discussed in context with solid solution hardening due to elastic interactions of solute atoms with gliding dislocations and ordering effects. Die Vickers-Eindruckharte von H1-xgCdx Te- Mischkristallen wurde als Funktion der Zusammensetzung x an einkristallinen Bridgman- und THM-Proben und an polykristallinem Ausgangsmaterial bei Zimmertemperatur gemessen. Die Mikroharte lag zwischen 220 MPa fur x = 0 und 440 MPa fur x = 1, besitzt ein Maximum von 850 MPa bei x ∼ 0.75 und unterschied sich zwischen ein - und polykristallinen Proben. Der Hartungseffekt dH/dx hangt stark von der Zusammensetzung ab und wird im Zusammenhang mit einer Mischkristallhartung infolge elastischer Wechselwirkungen der gelosten Atome mit Gleitversetzungen und mit Ordnungseffekten diskutiert.

Characteristic of the photoconductivity of thallium monoselenide

Abstract: Systematic investigations on thallium monoselenide single crystal photoconductivity were reported at 300 K as a function of excitation intensity, side illumination, and wavelength. The samples were prepared using Bridgman technique. The photoconductivity as a function of the modulation frequency of the incident light was plotted at different values of light intensity. The effect of light intensity on the photocarrier lifetime was studied. The relation between the photocurrent and applied voltage at different values of light intensity was represented graphically. Side illumination effect in all these relations was checked. The spectral distribution of the photoconductivity of TlSe in the spectral region 1.24 ev to 1.77 ev was measured, and the energy gap was evaluated. All results were discussed and analyzed. Studies for such samples are very important and necessary in order to understand their use as photoconductor.

MOCVD layer growth of ZnO using adducts of dimethyl‐ and diethylzinc

Abstract: Reaction mixtures of the tetrahydrofuran adducts of Zn(CH3)2 and Zn(C2H5)2 with tertiary butanol are very well suitable for the MOCVD of c-axis oriented ZnO films. The deposition process is greatly determined by the kind of the gas inlet into the vertical reactor. The growth rates present a great dependence on temperature. The incorporation of compensating copper acceptors can be achieved with the help of cyclopentadienyl (tributylphosphine)-copper (I). The structural and the electrical properties of the films are presented.

The influence of controlled electron-seeking addition agents of the melt on stilbene single crystal structure and radioluminescence properties

Abstract: The study of certain radioluminescence characteristics of stilbene single crystals is performed. Doping the stilbene melt with electron-seeking (ES) addition agents of benzol and benzophenone halogen derivatives allowed to control the structure perfection of the crystal grown. The root-mean-square random orientation of single crystal mosaic structure, and concentration of the deep traps of charge carriers and excitons were minimum for the single crystals grown from the melt containing 0.1 mol% ES addition agent. Doping the melt with ES addition agents did not cause the appearance of additional luminescence impurity centres or quench luminescence centres in the single crystals grown. [Russian Text Ignored].

Optical properties of flash‐evaporated CuInTe2 thin films

Abstract: Optical absorption spectra of flash-evaporated polycrystalline thin films of CuInTe2 are measured in the photon energy range from 0.5 to 3.0 eV. A gap energy in the range from 0.96 to 0.99 eV and a spin-orbit splitting of the valence band of 0.61 ± 0.03 eV are derived from the spectra. It is found that the spectra are considerably influenced by grain boundary effects. Optische Absorptionsspektren von durch Flash-Verdampfung hergestellten dunnen CuInTe2-Schichten wurden im Photonenenergiebereich von 0.5 bis 3,0 eV gemessen. Aus den Spektren wird eine Breite der verbotenen Zone im Bereich von 0,96 bis 0,99 eV und eine Spin-Bahn-Aufspaltung des Valenzbandes von 0,61 ± 0,03 eV ermittelt. Es zeigt sich, das die Spektren merklich durch Korngrenzeneffekte beeinflust werden.

The twisting of LiNbO3 single crystals grown by the Czochralski method

Abstract: As a result of our experimental work of mainly practical importance we established that for LiNbO 3 single crystals the Mg and Fe dopants promote spirality whereas decreasing of the pulling velocity strongly reduces the propensity of the system to produce spiral-shaped crystals

X‐ray powder diffraction investigations of solid solutions in the KClKBrH2O system at 298 K

Abstract: The measurements of crystal lattice parameters (a) of solid solutions being formed in the system KClKBrH2O at 298 K were conducted. The volumes (v) of unit cells and the densities (ϱ) of mixed crystals K(Cl, Br) were calculated. It was confirmed that in the investigated system continuous solid solutions were formed. The lattice parameters of these crystals formed from aqueous solutions of salts as well as from molten salts and also calculated by Durham-Hawkins method were nearly identic. Es werden die Gitterparameter a der Mischkristalle im System KClKBrH2O gemessen und das Volumen der Elementarzelle v und die Dichte ϱ der Mischkristalle K(Cl, Br) berechnet. Es wird bestatigt, das in dem untersuchten System die Kristalle luckenlose Mischungen bilden. Die Gitterparameter dieser Kristalle, die sowohl aus waseriger Salzlosung oder Salzschmelzen gewonne wie auch nach der Durham-Hawkins-Methode berechnet werden, sind annahernd gleich.

Zeolite NaCaA as a desulphurization adsorbent – modification of its thermal and hydrothermal stability

Abstract: The thermal and hydrothermal stability of the zeolite NaCaA in dependence on the ion exchange degree have been investigated. The increasing thermal stability of the zeolite with increasing content of calcium ions corresponds to the higher stability of calcium silicates compared with sodium silicates. In contrast to that the decreasing hydrothermal stability is due to the decreasing alkalinity of the zeolite in aqueous media. Measurements of the pH-value of zeolite/water slurries underline this tendency. Es wurde die thermische und hydrothermale Stabilitat des Zeoliths NaCaA in Abhangigkeit vom Kationenaustauschgrad untersucht. Die wachsende Zeolithstabilitat mit steigendem Gehalt an Calciumionen korrespondiert mit der hoheren Stabilitat von Calcium-Silicaten im Vergleich zu Natrium-Silicaten. Im Gegensatz dazu ist die sinkende hydrothermale Stabilitat eine Folge der abnehmenden Alkalitat der Zeolithe im wasrigen Medium. Messungen des pH-Wertes von Zeolith/Wasser-Suspensionen dokumentieren diesen Befund.

On the morphological instability of the growing crystals (IV). The effect of supersaturation inhomogeneity upon the morphological stability of KDP single crystals

Abstract: The diffusion-induced inhomogeneity in the supersaturation on close packed faces of KDP crystals, growing from aqueous solutions has been investigated. The interferometrically found values of the concentration difference on the crystal edge and in the centre of the most closely packed face {100} were compared with the theoretically expected concentration nonhomogeneities calculated by means of CHERNOV's formula. The comparison has been performed especially for the moment when the KDP crystals lose the stability of their polyhedral shape and gradually acquire a skeletal form. A fairly good coincidence was found. Die diffusionsbedingte Ubersattigungsinhomogenitat auf den dicht gepackten Flachen von aus wasrigen Losungen wachsenden KDP-Kristallchen wurde untersucht. Der interferometrisch bestimmte Konzentrationsunterschied auf den Kristallkanten und in der Mitte der dichtest gepackten Flachen {100} wurde mit der theoretischen, nach der CHERNOV-schen Gleichung gerechneten Konzentrationsinhomogenitat vergliche. Dieser Vergleich wurde besonders fur den kritischen Wachstumsmoment durchgefuhrt, in welcher die KDP-Kristallchen die Stabilitat ihrer polyedrischen Form verlieren und dann allmahlich eine Skelettform annehmen. Dabei wurde eine recht gute Ubereinstimmung gefunden.

Hydrothermal synthesis of (Zr0.33 Ti0.67) O2–srilankite in the system ZrO2TiO2H2OMF; (M = Na, K)

Abstract: The hydrothermal synthesis in the system ZrO2TiO2H2OMF; (M = Na, K) is discussed for the temperature range 573 K–773 K and the pressure of 100 MPa to 150 MPa. Starting with Zr- and Ti- butoxides their co-precipitated hydrolysates which had been annealed in different ways were used as initial products. The formation of mixed crystals (Zr, Ti)O2 analogous to the rare mineral srilankite was dependent on the crystallinity and homogeneity of the initial products. 573 K and 100 MPa proved to be the most favourable conditions for synthesis. Higher temperatures (773 K) produced multiphase crystallizates of (Zr, Ti)O2, baddeleyite, anatas, and rutile.