N. N. Faleev

Fractal structure of ultradisperse-diamond clusters

Ultradisperse-diamond clusters are shown to be fractal objects, and the character of variation of the fractal dimension in the course of the diamond-graphite phase transition under annealing in an inert atmosphere is studied.

Enhanced arsenic excess in low-temperature grown GaAs due to indium doping

We have found that isovalent indium doping enhances arsenic excess in GaAs films grown by molecular beam epitaxy at low temperature. An increase in lattice expansion and near infrared optical absorption, as well as higher density of As clusters, have been observed in the indium-doped films when compared to the conventional indium-free ones.

INFLUENCE OF LONG-RANGE LATERAL ORDERING IN STRUCTURES WITH QUANTUM DOTS ON THE SPATIAL DISTRIBUTION OF DIFFRACTED X-RAY RADIATION

Perfectly crystalline (InAs–GaAs) multilayer periodic structures on (001) GaAs, which contain InAs quantum dots (QDs), have been studied by high-resolution X-ray diffraction. It has been shown that the existence of such scattering objects as QDs strongly influences X-ray diffraction, changing the spatial distribution of scattered radiation. Additional long-range ordering in layers containing QDs results in unusual and significant elongation of superlattice and substrate reflections in the qx direction. A novel qualitative model of scattering layers consisting of perfect InAs and GaAs coherent clusters has been developed.

High-resolution x-ray diffraction study of InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature

InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature are investigated by high-resolution x-ray diffractometry. It is shown that despite a very high density of point defects due to the presence of excess arsenic, the as-grown superlattice has high crystal perfection. An analysis of the changes in the x-ray diffraction curves shows that high-temperature annealing, which is accompanied by the formation of As clusters and diffusion of indium, produces significant structural transformations in the GaAs matrix and at the interfaces.

X-Ray diffraction analysis of multilayer InAs-GaAs heterostructures with InAs quantum dots

Multilayer InAs-GaAs structures with an array of vertically aligned InAs quantum dots in a GaAs matrix, grown by molecular-beam epitaxy, were investigated by crystal truncation rods and high-resolution x-ray diffractometry methods. It was shown that the formation of scattering objects such as vertically aligned quantum dots in the structures strongly influences the mechanism of diffraction scattering of x-rays and changes the spatial distribution of the diffracted radiation. This is explained by the appearance of additional long-range order in the lateral arrangement of the scattering objects in the periodic structures, by the curving of the crystallographic planes in the periodic part of the structure, and by the quasiperiodicity of the deformation profile due to the vertically coupled quantum dots. The observed spatial distribution of the diffracted intensity can be explained qualitatively on the basis of a new model where the scattering layers with quantum dots consist of defect-free, coherently coupled, InAs and GaAs clusters.

Anisotropy of the spatial distribution of In(Ga)As quantum dots in In(Ga)As-GaAs multilayer heterostructures studied by X-ray and synchrotron diffraction and transmission electron microscopy

High-resolution X-ray and synchrotron (crystal truncation rods) diffraction methods and transmission electron microscopy have been employed to study MBE-grown multilayer In(Ga)As-GaAs heterostructures with arrays of vertically coupled In(Ga)As quantum dots (QDs) in a GaAs matrix. Additional (vertical and lateral) spatial ordering of QDs in perfect crystalline structures, giving rise to undulations of the crystalline planes and quasi-periodic elastic strain, was shown to be essentially anisotropic with respect to crystallographic directions of the [110] type. The anisotropy of the QD formational system of can be accounted for by assuming that the spatial ordering of the QDs and the corrugation of the crystal planes are the initial stages of relaxation of the elastic strain introduced into the system by the QDs. The anisotropic relief of the crystal planes (corrugated growth surface) results from the formation of a system of spatially ordered quantum quasi-wires uniformly filled with QDs. In a multilayer heterostructure with high crystal perfection, the anisotropic relief of the crystal planes is inherited by overlying layers and its amplitude decreases gradually with increasing distance from the source of elastic strain—the superstructure containing In(Ga)As QDs in the given case.

Applications of dynamical theory of X-ray diffraction by perfect crystals to reciprocal space mapping

Komi Research Center, Ural Division, Russian Academy of Sciences, Syktyvkar, 167982, Russian Federation, Syktyvkar State University, Syktyvkar, 167001, Russian Federation, School of Science and Technology, University of New England, NSW 2351, Australia, School of Physics and Astronomy, Monash University, VIC 3800, Australia, and Ira Fulton School, School of ECEE, Solar Power Laboratory, Arizona State University, 7700 South River Parkway, Tempe, AZ 85284, USA. *Correspondence e-mail: vpunegov@dm.komisc.ru

Influence of mismatch of the lattice parameters on the structural, optical, and transport properties of InGaAs layers grown by molecular beam epitaxy on InP(100) substrates

The influence of mismatch stress on the structural, optical, and transport properties of thick InGaAs layers grown on InP(100) substrates by molecular-beam epitaxy is investigated. It is found that layers having tensile stress can be grown with a greater mismatch than compressively stressed layers before plastic relaxation sets in. The critical mismatch for thick InGaAs layers is not described with sufficient accuracy by either the mechanical equilibrium model or the energy balance model. The range of mismatches required to obtain high carrier mobilities and high radiative recombination efficiencies in InGaAs layers grown on InP substrates is much narrower than the pseudomorphic growth range. The maximum mobilities and minimum widths of the photoluminescence peak are attained in layers matched with the substrate in terms of the lattice parameter and also in slightly gallium-enriched layers. The compositional dependence of the width of the band gap is investigated with allowance for the influence of stress.

Correlation between the reliability of laser diodes and the crystal perfection of epitaxial layers estimated by high-resolution x-ray diffractometry

The dependence of the degradation of high-power quantum-well GaAs/AlGaAs laser diodes, grown by molecular-beam epitaxy, on the crystal perfection of the individual layers of the heterostructure is investigated. The crystal perfection of the layers is estimated by highresolution x-ray spectrometry. A numerical fit of the diffraction-reflection curves is performed using the Debye-Waller static factor. It is shown that considerably higher crystal perfection of laser heterostructures can be obtained by using as the waveguide layers binary AlAs/GaAs superlattices instead of the solid solution AlGaAs.

Specific Aspects of X-Ray Diffraction on Statistically Distributed QDs in Perfect Crystal Matrix

Crystalline (InAs-GaAs)/GaAs (001) multilayer periodic structures containing InAs quantum dots (QDs) have been studied by SR-CTR (Synchrotron Radiation - Crystal Truncation Rod) and RSM (Reciprocal Space Mapping) methods. The appearance of a lateral long-range order in InAs-GaAs QDs has been demonstrated. A qualitative model of investigated structures has been suggested, within which the static Debye-Waller factor has been obtained. Using a new statistical approach considering semidynamical X-ray diffraction allows both the CTR and RSM data to be simulated. The principal parameters of the investigated structures have been determined by means of a fitting procedure.