Study of Thin Films of High Temperature Superconductors Based on YBaCuO by EPMA

 An analytical model of an effective atomic number, Z _eff, for simultaneous calculation of composition and thickness of films on substrates that allows for backscattering processes is presented. Comparison of dependencies of ϕ(ρz) parameters for film elements on electron beam energy, on atomic numbers of a film and a substrate and on film thickness was done. The errors inherent in EPMA have been determined by comparing experimental data obtained on YBa₂Cu₃O_7−x bulk crystals with model calculations. Possibility of EPMA as an effective technique for investigation of spatially inhomogeneous objects was demonstrated by studying the correlation between composition and local superconducting properties (values of critical temperature and critical current) of these films.     

Domain structure of GaN/SiC-based materials for semiconductor lasers

The domain structure of GaN/SiC hexagonal semiconductor films has been studied using small-angle X-ray scattering in order to determine possible domain configurations in a GaN/SiC film that can influence the properties of the laser on its basis. Data on specific features of the samples, such as geometrical properties of clusters and the distances in superstructures (layers, superlattices), respectively, have been obtained by the processing of the small-angle X-ray scattering spectra according to Porod’s and Bragg’s models. A model of regular network of domain walls in GaN/SiC film has been proposed. The hypothesis on the formation of filamentary structures near the film-substrate interface has been confirmed.     

Integrated characterization of multilayer periodic systems with nanosized layers as applied to Mo/Si structures

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.     

Method for calculating the monochromatic field in a layered medium

An approximate method is proposed for calculating the monochromatic field described by the wave equation in a layered medium. The method is based on the use of the equivalent propagation constant and makes it possible to reduce the computation time as compared to other methods based on the strictly dynamic approach. The range of correct application of the method is estimated for the problems for which the exact solution is known.     

Electron-beam microprobe analysis of epitaxial GaxIn1−xP solid solutions

Ga_xIn_1–xP epitaxial layers were investigated by means of a scanning electron microscope X-ray microanalyser. The conditions for quantitative X-ray microprobe analysis are discussed. The growth of Ga_xIn_1–xP layers is possible on GaP substrates with x > 0,8 and on GaAs with 0,3 < x < 0,6. For the deposition of layers with 0,5 < x < 0,8 two substrate materials are possible: GaAs_1–xP_x or Ga_xIn_1–xP with suitable compositions. These materials must be epitaxially deposited by step by step layer growth or by vapour phase epitaxy, respectively.     

Investigation of the structure and luminescence properties of CdF2-CaF2 : Eu superlattices on Si(111)

A complex investigation of CdF₂-CaF₂ : Eu superlattices with different bilayer thicknesses (2.0–17.5 nm) grown by molecular beam epitaxy on Si(111) has been carried out. The structural perfection of the layers and interfaces of the superlattices have been estimated from the X-ray diffractometry and reflectometry data. The possibility of producing short-period pseudomorphic superlattices with a period of approximately 2 nm has been established. It has been shown that these superlattices are characterized by a larger root-mean-square roughness amplitude of the interfaces as compared to the long-period superlattices. The specific features of cathodoluminescence spectra have been analyzed as a function of the superlattice period. It has been revealed that, with a decrease in the superlattice period, the intrinsic luminescence intensity of fluorides increases in comparison with the intensity of the luminescence associated with the emission of Eu²⁺ impurity ions; in this case, several Eu³⁺ luminescence bands appear in the spectrum. The possibilities of electron probe microanalysis for determining the ratio of thicknesses of individual layers in short-period superlattices have been demonstrated.     

Process of fabricating semiconductor microcavities and photon crystals

A process of fabricating microcavities and photon crystals in GaAs structures by means of electron lithography and reactive ion etching is described. Two types of structures, with micropillars and with photon crystals, are considered. The latter structures have the form of a square or hexagonal array of holes in a planar waveguiding structure. The minimal diameter of the micropillars is 100 nm, and their height is 700 nm. The size of the holes in the photon crystals and the photon crystal period are controllably varied from 140 to 500 nm and from 400 to 1000 nm, respectively. The etch depth of the crystals is more than 350 nm.     

TEM study of the structure of gallium nitride epitaxial films grown on substrates with different interface morphologies

The structure of gallium nitride epitaxial layers grown on patterned substrates was studied by transmission electron microscopy. The engraving of a substrate surface with pits or pyramids undoubtedly leads to structural improvement. The best results are obtained at a pattern density of about 10⁷ cm^?2.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.