Polycrystallinity in Gallium Arsenide Crystals Grown by the Czochralski Method

Crystallography Reports - The specific features of the formation of crystallites in gallium arsenide crystals grown by the Czochralski method have been investigated. The crystallites are found to...     

Identification of dislocations and their influence on the recombination of charge carriers in gallium nitride

The relation between the density of etch pits revealed in GaN by etching in a KOH/NaOH eutectic and the density of dislocations determined by transmission electron microscopy (TEM) is studied along with the relation between the density of dislocations and the density of dark spot defects observed in GaN by microcathodoluminescence (MCL) and electron-beam-induced current (EBIC). It is demonstrated that selective etching is a reliable rapid method for the determination of the type and density of dislocations in GaN in the range 10⁶–10⁸ cm^?2, while MCL and EBIC can be used for the rapid nondestructive determination of the density of dislocations in the range 10⁶–10⁸ cm^?2. It is also found that some deep electron and hole traps are related to dislocations.     

Formation of Facets in GaAs Crystals Doped with Sn and Te during the Growth by the Czochralski Method

Crystallography Reports - Facets are formed at the periphery of the conical part of GaAs single crystals grown by the Czochralski method when the melt is supercooled at the crystal periphery. The...     

Defect formation in Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>/Ge(111) epitaxial heterostructures

Selective chemical etching and transmission electron microscopy are used to study the defect formation in Ge_1?xSi_x/Ge(111) epitaxial heterostructures at 0.01<x<0.35. As the Si content in the solid solution (SS) increases, the dislocation densities in the epitaxial layer, at the interface, and in the near-interface region in the substrate are found to vary nonmonotonically. The difference in the depth distribution of dislocations observed in the heterostructures in three different SS composition ranges is caused by the effect of the SS composition on the kinetics of misfit-stress relaxation, in particular, on the intensity of misfit-dislocation generation and multiplication. It is found that, in the heterostructures grown by hydride epitaxy at 600°C, misfit-dislocation multiplication through a modified Frank-Read mechanism occurs only in the range 0.03<x<0.20. The results obtained are explained in the context of the effect of silicon-rich microprecipitates, which form during the spinodal decomposition of the SS, on dislocation generation and motion in the epitaxial layer. A mechanism is proposed for misfit-dislocation generation by heterogeneous sources in the epitaxial layer; the mechanism is based on the generation of interstitial dislocation loops near microprecipitates.     

Magnetoplastic Effect in Te-Doped GaAs Single Crystals

Crystallography Reports - The influence of a dc magnetic field on the motion of growth dislocations with a density of (0.7–7.0) × 104 cm–2 and the electron density in the range of...     

Effect of a Travelling Magnetic Field on the Parameters of Tellurium-Doped Gallium Arsenide Single Crystals Grown by the Czochralski Method

Crystallography Reports - The effect of a traveling magnetic field on the parameters of Te-doped GaAs single crystals in the carrier density range of 5 × 1017–2 ×...     

Experimental demonstration of coherent coupling of two quantum dots

During the recent years semiconductor nanostructures have attracted considerable interest with respect to potential applications in quantum information processing. In particular, quantum dot molecules have been suggested to provide the building block of a quantum computer: forming quantum gates due to coherent coupling of two dots. The characteristic dependence of the splitting of ‘bonding’ and ‘anti-bonding’ states suggests coherent coupling of two InAs/GaAs quantum dots. Anti-crossings in the fine structure of excitons due to mixing of optically bright and dark states have been observed in Faraday configuration. In Voigt configuration the diamagnetic shift of the quantum dot molecule is enhanced compared to a single quantum dot. These findings altogether demonstrate the coherent coupling of exciton states in quantum dot molecules.     

β-Galactosidase from <Emphasis Type="Italic">Penicillium canescens</Emphasis>. Properties and immobilization

β-galactosidase from Penicillium canescens was immobilized on chitosan, sepharose-4B, foamable polyurethane and some other carriers. The highest yield of immobilization (up to 98%) was obtained by using chitosan as a carrier. The optimum pH and temperature were not significantly altered by immobilization. High stability of immobilized β-galactosidase during storage was demonstrated. Efficient lactose saccharification (over 90%) in whey was achieved by using immobilized β-galactosidase.     

Raman spectroscopy study of the structure of gallium nitride epitaxial layers of different orientations

The composition nonstoichiometry and structural quality of undoped gallium nitride layers grown by the hydride vapor phase epitaxy on sapphire substrates of different orientations have been estimated using Raman spectroscopy. It is found for the first time that the peak position of the phonon mode E₂(high) in the Raman spectra of gallium nitride films at a wave vector of 572 cm^–1 depends on the initial orientation of sapphire substrate and is low-frequency shifted when passing from Ga-polar to partially N-polar orientation. Additional modes are found in the spectra of GaN layers grown on substrates with m and r orientations. It is shown that a decrease in the composition deviation from stoichiometry, caused by reducing the HCl flow through the gallium source during the growth of GaN layers, leads to an increase in the phonon-mode intensity in the Raman spectrum.     

Thermally stimulated relaxation of misfit strains in Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(100) heterostructures with different buffer layers

The regularities of the defect formation in Si_1−x Ge_x/Si heterostructures (x = 0.15 and 0.30), consisting of a low-temperature Si buffer layer and a SiGe solid solution, during their growth and subsequent annealings at temperatures 550–650°C are investigated by the methods of optical and transmission electron microscopy and X-ray diffraction. It is shown that the misfit-strain relaxation by plastic deformation under the conditions studied occurs most intensively in heterostructures with low-temperature SiGe buffer layers. The maximum degree of misfit-strain relaxation (no higher than 45%) is observed in the heterostructures with x = 0.30 after annealing at 650°C. The results obtained are explained by the effect of the nature and concentration of dislocation-nucleation centers, existing in low-temperature buffer layers, on the characteristics of the formation of a dislocation structure in the heterostructures under consideration.