Beitrag zur Kristallisation von ZnSiP2 aus der Gasphase

The influence of thermal conditions on the synthesis and crystallinity of ZnSiP₂ is investigated. Extensive measurements lead to statements on the axial and radial distribution of temperature in the apparatus and in the reaction vessel. The axial temperature gradient in the crystallization room equals some 3 deg/cm, whereas in the ampoule a radial gradient of 4 to 5 deg/cm is ruling. — At different temperature differences the thermal conditions of deposition of ZnSiP₂ are discussed, and it is found that ΔT should not fall below a minimum value of 15 deg, if ZnSiP₂ is to be produced by means of gas phase transport in a finite period of time. — In a full discussion the characteristic transport effects are explained. — Condensation of ZnP₂ at the end of the ampoule and by secondary transport caused by local temperature and concentration gradients in the crystallization room are stated to be responsible for different concentration profiles, for the phases present and for the crystallinity depending on the place of crystallization. — Hints for favourable variants of growing are given.     

Zur Bestimmung des effektiven Verteilungskoeffizienten von Te bei der Züchtung von GaP-Einkristallen aus nichtstöchiometrischen schmelzen

An equation for determining the effective distribution coefficient, k_eff, under the conditions of growing single crystals from non-stoichiometric melts is proposed. This equation is used for the calculation of k_eff at Te concentrations in the melt from 3.5 × 10⁻³ up to 9.1 × 10⁻² at.%. From numerous measurements a k_eff value of 0.070 with the 1 σ boundaries at 0.116 and 0.043 is found. The relatively wide spread is accounted for by the heterogeneous distribution of doping material which is due to the technique applied and to the polar properties of the GaP lattice.     

Ein Beitrag zur Züchtung von Alkalihalogeniden aus Lösungen

The authors performed preliminary investigations on the possibility of lowering the inclination of alkali halides to nucleation during crystallization from aqueous solutions. The increase of the metastable region and lowered inclination to nucleation was investigated by means of influencing the degree of order of the solution. It was proved that in the presence of dissolved oxygen, with higher concentration of hydrogen ions and in the absence of visible light the inclination to nucleation can be considerably lowered.     

Zur Züchtung von β-Kupferphthalocyanin-Einkristallen aus der Gasphase

An apparatus useful for many kinds of vapour phase growth used in order to clarify reasons for bad reproducibility and constancy of growth conditions by an growing method known since 1936 and reasons for cavity growth. The characteristics of growth are described dependent on different growing methods and on various kinds of nucleation and crystal growth. The introduction of new growing methods allows the production of larger crystals. The growth of the needle-like crystals is governed by diffusion. The shape of the crystals does not differ qualitatively from their equilibrium shape. The crystals grow with smooth surfaces. Only the front surfaces show morphological imperfections, if the crystals exceed a critical size.     

Untersuchungen zur Neubildung von Versetzungen bei der tiegelfreien Züchtung von Silizium-Einkristallen

During the crucible free growing of dislocation free silicon monocrystals frequently spontaneous generations of new dislocations are observed which cannot be attributed to perceptible reasons. By means of X-ray topographic and metallographic methods it is tried to localize the origin of these dislocation generations in the crystal. Their generation in areas of the crystal surface permits to suppose the existence of a temperature stress mechanism, which releases the generation of new dislocations in the plastic regions of the just formed crystal in consequence of high shocks of stress.     

Oberflächenstörungen und Hohlwachstum bei der Züchtung von β-Kupferphthalocyanin-Einkristallen aus der Gasphase

Hollow crystals are obtained frequently during the growth of copper phthalocyanine single crystals from the vapour phase. This appearance makes some physical investigations impossible. To overcome these difficulties some ways are discussed. The reasons for hollow growth are instabilities in the growth caused by diffusion controlled inhomogeneities in supersaturation on the growth front. This was found by observations of surface defects and by defined growth experiments. By introduction of special methods of growth and use of defined parameters one obtains bulk crystals of larger extent up to 1 mm in cross direction. References are given in the field of hollow crystal growth in the vapour phase of other substances.     

Zum Wachstum von AIII-BV-Verbindungen aus nichtstöchiometrischen Schmelzen (III) Untersuchungen zur Flächenmorphologie homoepitaktischer GaAs-Schichten

The morphology of a surface with the formation of GaAs-layers from Ga solutions is caused by the primary formation of characteristic holes. The reason for the origin of such holes is explained by small stresses resulting from small lattice mismatches.     

Über die Züchtung von ZnS-, ZnSe- und ZnTe-Einkristallen unter Anwendung der chemischen Transportreaktion

In connection with investigations on the synthesis of ZnS, ZnSe and ZnTe single crystals by chemical transport using iodine as transport agent in sealed tubes the mechanism of mass-transport and the relationship between material-transport and growth process were studied. In this way the optimum conditions for growing single crystals were found. The dependence of the transport rate on the undercooling ΔT, on the diameter of the ampoule and on the pressure in the system is described. Relative large crystals in good quality could be propared by influencing the nucleation and the growth process by help of well defined transport rates. In all cases crystals with sphalerite structure only were obtained. The habit with the most common faces (110), (111) and (211) was found to be predominant. The dominant habit is responsive to variations in the experimental parameters. The crystal perfection have been determined by etch patterns and by X-ray topography.     

Zum Wachstum von AIII-BV-Halbleitern aus nichtstöchiometrischen Schmelzen (I) Wachstum von GaAs auf GaAs bei konstanter Temperatur

A method for the preparation of GaAs layers of different thickness on GaAs from solutions of Ga at constant temperatures is described using inner cooling of the substrate holder by a gas flow. The dependence of the growth rate on the intensity of inner cooling, movement of the substrate holder, and on growth temperature is given and explained. Furtheron is shown that constitutional supercoolung can be avoided by means of a suitable temperature profile and absence of periodic temperature fluctuations.     

Abscheidung von Cu2O aus der Gasphase im strömenden Medium

CVD-experiments in the system Cu O H Cl N result in the growth of Cu₂O single crystals. The characteristic faces of the various forms are the {100} ones. A thermodynamic analysis permits to predict such conditions under which Cu₂O is deposited without deposition of any other phases.     

Untersuchungen zur heteroepitaktischen Abscheidung von GaP auf GaAs aus der Sn-Lösung

The used liquid-phase epitaxy apparates are described and the experimental conditions of growth on GaP and Ga(AsP) onto GaAs-substrates are reported. The influence of growing conditions (temperature, cooling rate, composition of melt) on the quality of interface and on the inlusion of solvent are discussed. The consequence of varying degrees of substrat-misorientation on the surface morphology has been studied.     

Beitrag zur Verteilung der Hauptkomponenten bei der Darstellung von AIIBIVC2V-verbindungen mittels Gasphasentransports,dargestellt am Beispiel von ZnSiP2

Results obtained in preparing ZnSiP₂ by means of gas phase transport have indicated so far that concentration profiles of the main components exist in the crystallization zone. The crystalline deposit grown by use of ⁶⁵Zn was analyzed radiometrically and metallographically. Concentration differences between the crystals were found to exist and determined as a function of the place of crystallization, and the zinc content in the direction of the crystal centre was measured. An increasing zinc concentration towards the end of the ampoule and in the direction of the crystal centre was found to be typical. The presence of binary phases was established. Attempts were made to equalize concentrations by subsequent thermal treatment and multiple transport, and different results were obtained.     

Zum Wachstum von AIIIBV-Halbleitern aus nichtstöchiometrischen Schmelzen (II) Dotierung von GaAs und Ga1−xAlxAs mit Zink

Doping of GaAs and Ga_1−xAl_xAs with Zn in the LPE process was studied by a radioanalytical method. It is found that Zn diffuses from the Ga-(Al)-As-Zn-solution into the n-GaAs substrate before epitaxial growth starts. This “pre-diffusion” and the following diffusion of Zn out of the epitaxial layer into the substrate results in three regions with distinct Zn-graduation in the vicinity of the pn-junction. There are no striking differences for GaAs/GaAs and Ga_1−xAl_xAs/GaAs structures. The Zn concentration in GaAs epitaxial layers decreases exponentially from the substrate up to the layer surface. From this profile the temperature dependence of the Zn segregation coefficient is calculated. At 900°C a value k_eff = 5,2 · 10⁻² is found. The doping profile in Ga_1−xAl/As layers is more complex. It is influenced by the changings of temperature during the growth of the layer and by the nonuniform Aldistribution over the layer thickness.     

Berechnung der Übersättigung bei der Kristallisation von InAs aus der Gasphase

It is proved that under experimental conditions for the growing of InAs crystals from the vapour phase the partial supersaturation of indium monoiodide corresponding to the difference of partial pressure of InJ_(g) in the source and in the crystallisation zones, can serve as a quantitative process parameter granting predictions on process development and results in a wide range of ruling conditions. Experiments confirmed the conclusions postulated on the base of quantitative analysis of the transport process. The analysis enables to controll the process parameters of crystal growth by chemical transport.     

Zur Anwendung elektrischer Analog-Modelle zur Bestimmung von Temperaturfeldern bei der Kristallzüchtung

Problems of heat conduction are of vital interest for crystal growing. Construction of a plant necessitates pre-knowledge on the corresponding temperature distribution to be expected on basis of geometry, material properties a.s.o. As these information are in general not easily gained by measurement of calculation, modelling by means of electric analogy is offered as a tool. Results are given, indicating that this method is not only simple and versatile, but also of sufficient accuracy.     

Untersuchungen zur röntgenografischen Verzerrungsverteilung von Versetzungen

For cylindrical crystallites with a dislocation on the axis are calculated deformation moments and with him the X-ray distribution function of deformations. The obtained deformation distributions deviates – except of special cases – from a Gaussian distribution, especially in the cases of the screw dislocation and the edge dislocation with inserted planes in interference position appears intense minimum values at small deformations and a dependence of all distributions on the Fourier order. – By the ratios of moments are compared the deformation distributions of dislocation models with the corresponding quantities of predetermined model distributions.     

Über das elektrolytische Wachstum und die Auflösung von Silbereinkristallen unter potentiostatischen Bedingungen. Einfluß der Zwillingsgrenzen

The rates of growth and dissolution of silver single crystals have been investigated under potentiostatic conditions. The results show that dissolution is more rapid than growth. That is explained with the effect of additional active centres in case of dissolution which have no noticeable influence on crystal growth rate. It is shown that twin boundaries have great influence on crystal growth rate. In the case of dissolution their effect is negligible and cannot be noticed. The asymmetry of the processes of growth and dissolution is stronger expressed in case of low values of potential, especially when crystals are of the normal type. The influence of twin boundaries on crystal growth rate increases with overvoltage.