Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals

Concentration and structural inhomogeneities in highly doped GaSb(Si) single crystals grown under various conditions of heat and mass transfer are studied by methods of X-ray topography, high-resolution X-ray diffractometry, and digital image processing. It is established that the inhomogeneity of crystals is determined by specific features of impurity microsegregation during growth under conditions of nonstationary convection in a melt and by peculiarities of the dislocation structure of crystals. The processes related to the initial stage of the decay of the Si supersaturated solid solution in GaSb contribute considerably to the inhomogeneity of crystals on the micro- and macrolevels.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)     

X-ray photoelectron spectroscopy study of cubic boron nitride single crystals grown under high pressure and high temperature

The defects, impurities and their bonding states of unintentionally doped cubic boron nitride (cBN) single crystals were investigated by X-ray photoelectron spectroscopy (XPS). The results indicate that nitrogen vacancy (V_N) is the main native defect of the cBN crystals since the atomic ratio of B:N is always larger than 1 before Ar ion sputtering. After sputter cleaning, around 6 at% carbon, which probably comes from the growth chamber, remains in the samples as the main impurity. Carbon can substitute nitrogen lattice site and form the bonding states of CBN or CB, which can be verified by the XPS spectra of C1s, B1s and N1s. The C impurity (acceptor) and N vacancy (donor) can compose the donor-acceptor complex to affect the electrical and optical properties of cBN crystals.     

Synthesis and characterization of germanium monosulphide (GeS) single crystals grown using different transporting agents

This paper reports the growth of germanium monosulphide (GeS) single crystals by vapour phase technique using different transporting agents. The single crystallinity and composition of the grown crystals have been verified by transmission electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX) respectively. Resistivity measurements have been carried out in different temperature ranges. Transport parameters, e.g. resistivity, Hall coefficient, carrier concentration and mobility have been measured at varying magnetic fields. All the experimental results have been explained.     

High resolution X-ray diffraction of GaN grown on Si (1 1 1) by MOVPE

High temperature GaN layers have been grown on Si (1 1 1) substrate by metalorganic vapor phase epitaxy (MOVPE). AlN was used as a buffer layer and studied as a function of thickness and growth temperature. The growth was monitored by in situ laser reflectometry. High resolution X-ray diffraction (HRXRD) revealed that optimized monocrystalline GaN was obtained for a 40 nm AlN grown at 1080 °C. This is in good agreement with the results of morphological study by scanning electron microscopy (SEM) and also confirmed by atomic force microscopy (AFM) observations. The best morphology of AlN with columnar structure and lower rms surface roughness is greatly advantageous to the coalescence of the GaN epilayer. Symmetric and asymmetric GaN reflections were combined for twist and stress measurements in monocrystalline GaN. It was found that mosaicity and biaxial tensile stress are still high in 1.7 μm GaN. Curvature radius measurement was also done and correlated to the cracks observations over the GaN surface.     

The effect of single A1GaN interlayer on the structural properties of GaN epilayers grown on Si （111） substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural properties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.     

X-ray diffraction study of Si(111)√3 × √3-Au

The structure of the Si(111)√3 × √3-Au surface has been investigated by the use of the surface X-ray diffraction with synchrotron radiation. The structure perpendicular to the surface was determined with respect to the Si bulk crystal. The results of least-squares analysis indicate that Au atoms are adsorbed on the Si substrate in which the first Si layer is missing. The heights of the Au layer and the Si second layer with respect to the intact Si third layer were estimated to be 3.09 ± 0.03 rA and 2.16 ± 0.10 rA, respectively. A possible model of the surface structure is proposed.     

Observation of Si(111) and gold-deposited Si(111) surfaces using micro-probe reflection high-energy electron diffraction

Observations of clean Si(111) and gold-deposited Si(111) surfaces have been performed using micro-probe reflection high-energy electron diffraction. It was found that many atomic steps on a Si(111) surface run in nearly the same direction, about 9° off the [1̄1̄2] direction. When gold was deposited on this surface at a substrate temperature of about 800°C, 5 × 1, diffuse √3 × √3R30°, sharp √3 × √3 R30° structures and Au clusters appeared on the surface with continuation of the deposition. During the deposition process, it was found that one kind of Si(111) 5 × 1 Au domain grew selectively along these atomic steps and nearly covered the entire surface. A phenomenon of gold clusters moving during the deposition was also observed. These clusters all moved in nearly the same direction so as to climb the atomic steps.     

X-ray diffraction study of ion thermal vibrations in R2CuO4 (R=Pr and Gd) crystals

An X-ray diffraction study is reported of the symmetry in the spatial distribution of thermal vibrations of Cu₂₊, Gd³⁺, and Pr³⁺ ions in Gd₂CuO₄ crystals. An analysis of the pattern of the angular thermal-vibration amplitude distribution obtained experimentally at different temperatures allows a conclusion about the character of the local Jahn-Teller effect for the Cu²⁺ ions, structural phase transitions, and the orbital ground state of the Cu²⁺ ions.     

X-ray diffraction study of a structural phase transition in (NbSe4)3I

The second-order structural phase transition was observed by X-ray diffraction technique in (NbSe₄)₃I. The transition temperature (T_c) was 274.2 K. No evidence of the formation of the charge-density wave was found out. Temperature dependence of the intensity of (0,5,12) reflection obeys the Landau theory of the second kind of phase transition near T_c. Temperature dependence of the integral breadth of (0,0,12) reflection indicates the effect of the soft-phonon mode below T_c. The existence of the structural phase transition, probably not associated with charge-density-wave formation, suggests the unique nature of (NbSe₄)Z₃I in the new series of compounds (MSe₄)_xI (M=Nb, Ta).     

Mathematical modelling of heat and mass transfer under conditions of mixed convection in rectangular region with heat source and heat-conducting walls

Numerical modelling of a conjugate convective-conduction heat transfer in a rectangular region with a heat-release source was carried out in the presence of forced flow and mass exchange. The distributions of thermal and hydrodynamic characteristics, which describe the specific peculiarities of flow regimes under study, were obtained. The mutual influence of forced and free-convective flow was analysed. The scales of the effect of determining dimensionless complexes (Gr, Br, Re) on flow regimes were established. The evolution of analysed process was shown.     

A structural study of the A1-Ge(001) interface using total-reflected x-ray diffraction

Total-reflected x-ray diffraction of the A1-Ge(001) interface is analyzed by means of a simple theoretical model. The result suggests that the horizontal lattice constant of the initially deposited 30 ± 5 A1 layers changes gradually from 3.997 Å to 4.05 Å to accommodate the mismatch of the Ge and A1 lattice constants. The analysis also indicates that the A1 layer lattice is more disordered closer to the Ge substrate and is made up of ordered domains with an average size of 320 Å for all the A1 films prepared.     

Comparative studies of the features of the formation of impurity heterogeneity in GaSb:Te crystals in the case of directed crystallization under space and ground conditions

The results of comparative studies concerned with the formation of impurity heterogeneity in GaSb:Te crystals grown at the POLIZON facility by the Bridgman method under space and ground conditions are presented. Crystallization is carried out in the same temperature-time modes of the heaters: on board the Foton-M 3 spacecraft in space and by the vertical Bridgman method under conditions of weakened thermogravitational convection on Earth. In both cases, Marangoni convection is eliminated, and the effect of vibration microaccelerations on the ampoule that contains the melt is minimized. The microuniformity of the dopant distribution in the crystal areas that are recrystallized by the Bridgman method is higher than that in the seed grown by the Czochralski method. Microuniformity is higher under space conditions than under ground conditions with weakened thermogravitational convection. Spectral Fourier analysis of the spreading resistance distribution R _s reveals the characteristic periods of heat and mass transfer processes in the melts under ground and space conditions.     

Conjugate heat and mass transfer at gas-phase ignition of a cable line under current overload

The nonlinear nonstationary problem of heat and mass transfer at ignition of an overloaded cable line that penetrates from one room to another through a partition is numerically solved. Dependences of the ignition delay time of a mixture of oxidizer and thermal decomposition components of a cable sheath on the current load and also on the geometrical sizes and the partition material are found.     

Low-energy electron diffraction study of the reconstruction and orientational stability of Si(331)

Using low-energy electron diffraction, we have studied the reconstruction of Si(331). We find a previously unreported (12 × 1) reconstruction is characteristic of the clean surface; we present evident that a previously observed (13 × 1) reconstruction is not the equilibrium structure. The (12 × 1) reconstruction disorders via a strongly first-order phase transition at approximately 810°C. Heating carbon contaminated surfaces to about 950°C causes faceting to (111) and {17151} orientations.     

X-ray diffraction study of the effect of neutron irradiation on the defect formation in silicon crystals grown by the Czochralski method and annealed at high temperatures

The effect of x-ray scattering by neutron-irradiated and reference (unirradiated) silicon crystals grown by the Czochralski method and annealed at temperatures of 850–1050°C on the defect formation is comparatively investigated using triple-crystal x-ray diffractometry. The sizes and concentrations of clusters composed of point defects and dislocation loops formed during decomposition of an oxygen-containing solid solution and subsequent clusterization of the point defects are calculated.     

X-ray photoelectron diffraction (XPED) patterns from: III-V compound mixed crystals (Ga1-xAlxAs AND GaAs1-yPy). Comparison of experiment and single scattering calculations

X-ray photoelectron diffraction (XPED) measurements, together with single scattering calculations, were made for two III—V group compound semiconductor mixed crystals (Ga_1-xAl_xAs(110) and GaAs_1-yP_y(001)). Each pair of photoelectrons excited at equivalent atomic sites in the crystal (Ga 3d and Al 2p in Ga₁-xAl_xAs, and As 3d and P 2p in GaAs₁-yP_y) showed essentially the same XPED patterns. Single scattering calculations reproduced the observed XPED patterns fairly well. An obvious site dependence of XPED patterns was observed in both the experimental and calculated results. These results clearly show that, for a given kinetic energy, XPED patterns mainly depend on the site of emitter atoms in the crystal, not on the species of emitter atoms. Thus, XPED measurements can be used for crystal site determinations in a fingerprint manner.