Zur Epitaxie von Galliumnitrid auf Korund im System GaCl/NH3/Ar

The vapour growth of single crystalline layers of GaN on {0001} oriented sapphire substrates in the temperature range of 500–1100°C is described for the system GaCl/NH₃/Ar. The RHEED micrographes of samples grown in the high temperature range of 1000–1050°C show KIKUCHI pattern, thus indicating a good crystalline perfection of the layers. The large free electron concentration of about 10²⁰ cm⁻³ decreases below 700°C rapidly with decreasing growth temperature. Simultaneously the crystalline perfection is remarcably lowered due to increasing misorientation of the subgrains, but no arcing of the RHEED spots due to polycrystalline behaviour is observed. The layers grown at 500°C are contaminated by chloride. Sometimes a dendritic overgrowth of the layers by the GaN sphalerite polytype takes place.     

Epitaxial growth of GaN on {1012} oriented sapphire in GaCl/NH3/He and GaCl/NH3/H2 systems

GaN epitaxial layers were grown on {101 2} sapphire substrates in the systems GaCl/NH₃/He and GaCl/NH₃H₂, respectively. The films obtained were investigated by light microscopy, RHEED method and electron-microscopical replica technique. The epitaxial relationship was found to be {101 2} // {112 0}_GaN; 〈112 0〉 // 〈101 0〉_GaN With respect to layer perfection the temperature range of 800 … 1060°C and growth rates ≧ 1 μm/min are the best growth conditions.     

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.     

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.     

Zur Bestimmung der Kristallitgrößenverteilung von Metallen auf Katalysatorträgern aus Röntgenweitwinkelmessungen (II). Direktberechnung von Kristallitgrößenverteilungen aus Röntgenbeugungsprofilen

Procedures are stated for the determination of the chord and the diameter distributions of metal crystallites in supported catalysts without differentiation directly as transformation of functions immediately derived from the intensities of wide angle X-ray interference lines. It is shown that the growth of the metallic crystallites can be described by means of the moments of the chord distribution. A kinetic equation of the second order was found for the growth of platinum on alumina in inert atmosphere and of the fourth order in oxidizing atmosphere.     

Zur anisotropen Dilatation von Fe3S4-Kristallen im elektrostatischen Feld

Synthetic crystals of Fe₃S₄ (greigite, spinel type, lattice constant 9.87 ÅU) extend by about 0.05 ÅU in an electrostatic field (field strength 860 volts · cm⁻¹) along the [111] axis in preference to any other directions. This property to be easily deformed makes it difficult to develop this crystallite (grain size about 300 ÅU) to a single crystal. It transforms into hexagonal pyrrhotite when cultivating it for crystal growth.     

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.     

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.     

Bildung von α-Martensit im Schnittbereich von ϵ-Martensitplatten

In steels the nucleation of crystals of α martensite from austenite is facilitated in the presence of ϵ martensite. Particularly within the range of crossing platelets of ϵ martensite with 〈110〉_γ direction α martensite is formed easily. That has been demonstrated by metallography in alloys with suitable composition and pretreatment. Also within the range of crossing of other shear products, as stacking faults or twins, the atomic arrangement for nuclei of α martensite is favourable. By the aid of matrices the strain in crossing 2 ϵ martensite plates, ϵ martensite plate and twin, and 2 twins resp., has been calculated and the result compared with the strain during the martensitic γ → α transformation.     

Zur Bestimmung der Kristallitgrößenverteilung von Metallen auf Katalysatorträgern aus Röntgenweitwinkelmessungen (I). Ermittlung primärer Verteilungskenngrößen aus Linienprofilen

Possibilities are investigated to determine the size distribution of metal crystallites in supported catalysts from wide angle X-ray interferences lines. It is shown that for this a Fourier method is suitable, which primarily provides the moments of the chord distribution. From the results distribution functions for the metal crystallites can be derived, which reproduce the experimental lines with high accuracy.     

Röntgenografische Untersuchung des Debye-Waller-Faktors und der Gitterkonstanten von V3Si-Pulver im Temperaturbereich von 25 K bis 1000K

The temperature dependence of the integrated X-ray diffracted intensities and the Bragg-angles in powdered V₃Si has been determined in the temperature range 25 K to 1000 K. The measured intensities could be described with an isotropic-quasiharmonic Debye-Waller-factor. An anomalous temperature dependence of the Debye-Waller-factor in the vicinity of the martensitic transition temperature could not be find. The temperature dependence of the linear thermal expansion below 100 K were observed to decrease rapidly with the temperature (and has a negativ sign below 70 K).     

Untersuchungen zum Einfluß von Temperatur und Versetzungen auf die integralen Röntgenintensitäten von Si-Einkristallen

It is possible to determine the Debye-temperature from measurements of the absolute integral X-ray intensities of silicon single crystals. Debye-temperatures of 543 to 533 K were found for a dislocation-free silicon crystal for temperatures between 90 and 296 K. The effect of dislocations on the Debye-temperature in silicon was investigated for various temperatures.     

Zur Gleichgewichts- und Wachstumsform von β-Kupferphthalocyanin-Einkristallen

The equilibrium shape of β-copper-phthalocyanine single crystals is obtained by the method of the PBC-vectors according to HARTMAN and PERDOK . These results agree well with the experimentally found growth shape of single crystals grown in the vapour phase. The crystals are of needle-like shape. The crystal surfaces are lattice planes of the kind {001}, {201 }, {100}, {101 } and {110}. The ratio of length to width of the crystals is influenced by the inert gas pressure during the growth process. This dependence is caused by the diffusion of the nutrient.     

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.     

Zur elastischen Wechselwirkung von Punktdefekten und Einschlüssen in der Nähe von Festkörperoberflächen

Calculating the interaction energy of point defects and inclusions in solids the influence of solid surfaces usually is neglected. But in the immediate vicinity of the boundary surfaces the deformations around the defects are, connected with a certain extra contribution to the total energy which was calculated applying continuum mechanics methods. The medium is assumed to be isotropic and homogeneous. An analytic expression for the interaction energy of two spherical inclusions near a half-room boundary surface is derived. The results show the interesting phenomenon that both attraction and repulsion between the defects occur, only depending upon the geometrical parameters.     

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.