Etch-pit studies of dislocations in indium antimonide

Indium antimonide specimens were plastically bent to introduce an excess of dislocations having either In-atoms at the edge of their extra half-planes or having Sb-atoms there. The lower yield stress for bending at 270°C was dependent on the direction of bend, being greater when specimens were bent to produce excess Sb-dislocations.Bent specimens were annealed and the etch-pit densities in them compared with theoretical prediction. It was found that a modified CP4 etch containing butylamine gives a reliable estimate of the total dislocation density (i.e. shows up both In- and Sb-dislocations), whilst the modified CP4 etch without butylamine reveals all the In-dislocations and about half the Sb ones.     

Growth, optical transmission and X-ray photoemission studies of BaB2O4 single crystals

Beta barium borate (-BBO) crystals have been grown by the top seeded solution growth technique (TSSG) using Na₂O as a flux. The crystals exhibited high transparency and the absence of inclusions and found to have sodium contamination in the range 150 to 230 p.p.m. The effect of this contamination on some crystal properties of interest has been investigated. The presence of impurities causes optical absorption below 550 nm in BBO crystals of both and -phases. X-ray photo emission spectroscopy (XPS) measurements performed on these crystals show that sodium gives rise to a measurable shift in the binding energies of the constituent ions. Further, the results show that Na⁺ ions enter into the lattice substitutionally and provide charge trapping sites close to the band edge.     

Probing bulk electronic structure with hard X-ray angle-resolved photoemission

Traditional ultraviolet/soft X-ray angle-resolved photoemission spectroscopy (ARPES) may in some cases be too strongly influenced by surface effects to be a useful probe of bulk electronic structure. Going to hard X-ray photon energies and thus larger electron inelastic mean-free paths should provide a more accurate picture of bulk electronic structure. We present experimental data for hard X-ray ARPES (HARPES) at energies of 3.2 and 6.0 keV. The systems discussed are W, as a model transition-metal system to illustrate basic principles, and GaAs, as a technologically-relevant material to illustrate the potential broad applicability of this new technique. We have investigated the effects of photon wave vector on wave vector conservation, and assessed methods for the removal of phonon-associated smearing of features and photoelectron diffraction effects. The experimental results are compared to free-electron final-state model calculations and to more precise one-step photoemission theory including matrix element effects.     

Oxidation study of polycrystalline InN film using in situ X-ray scattering and X-ray photoemission spectroscopy

Oxidation process of polycrystalline InN films were investigated using in situ X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The films were grown by dc sputter on sapphire (0001) substrates and were oxidized in air at elevated temperatures. The XRD data showed that the structure of the films changed to the bixbyite In₂O₃ (a = 10.11 Å) above 450 °C. Chemical configurations of the sample surfaces were investigated using high-resolution XPS. For the non-intentionally oxidized InN film, XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggests that indium and nitrogen are bound dominantly in the form of InN. An additional peak observed at 397.4 eV in the N 1s photoelectrons and the O 1s peaks indicate that the InN film surface is partly oxidized to have InO_xN_y configuration. After oxidation of the InN film at elevated temperature, the O 1s spectrum is dominated by In₂O₃ peak, which indicates that the structure is stable chemically with In₂O₃ configuration at least within the XPS probing depth of a few nm.     

Growth and characterization of indium antimonide and gallium antimonide crystals

Indium antimonide and gallium antimonide were synthesized from the respective component elements using an indigenously fabricated synthesis unit. Bulk crystals of indium antimonide and gallium antimonide were grown using both the vertical and horizontal Bridgman techniques. Effect of ampoule shapes and diameters on the crystallinity and homogeneity was studied. The grown crystals were characterized using X-ray analysis, EDAX, chemical etching, Hall effect and conductivity measurements. In the case of gallium antimonide, effect of dopants (Te and In) on transport and photoluminescence properties was investigated.     

X-ray photoemission study of Fe40Ni40B20 metallic glass

X-ray photoelectron spectroscopic (XPS) study of the valence band and the core levels of amorphous Fe₄₀Ni₄₀B₂₀ are presented. The oxides which formed at the surface of as-received sample are due to oxidation of iron and boron. For etched samples, the presence of oxide is not discernible, and the chemical environment is predominantly iron-boron-like, while nickel remains unassociated. The valence band has a high density of states at Fermi levels of amorphous Fe₄₀Ni₄₀B₂₀ are presented. The oxides which formed at the surface of B2s and Fe3d states, and metalloids-states respectively.     

Synchrotron X-ray topography study of defects in indium antimonide P-I-N structures grown by metal organic vapour phase epitaxy

InSb p-i-n structures were grown on an undoped InSb wafer in a horizontal metal organic vapour phase epitaxy reactor. 200 to 300 nm thick layers were fabricated using silane and zinc as dopant sources for the n-type and p-type layers, respectively. The defects of these samples were studied using synchrotron X-ray topography in large area transmission and transmission section geometries. Pendellösung fringes typical of a nearly perfect crystal were seen in the transmission section topographs. Large area transmission topographs showed dynamical diffraction images of voids and precipitates. Also straight and circular arc dislocations were observed. Most of the images seen in the topographs arise from the defects in the epilayers. Assuming that all precipitates and voids of the layer have been imaged the average precipitate and void density was calculated to be 4000 cm⁻² or 2 × 10⁸ cm⁻³ in the best sample.     

Monte Carlo simulation of X-ray photoemission electron microscopic image for Ag/Si nano-structure

With the development of the third generation synchrotron radiation sources the X-ray photoemission electron microscopy (XPEEM) is playing as a powerful tool for analyzing specimens with spatial resolution about tens of nanometer. It has been used to observe the chemical reaction process, and to investigate the surfaces, interfaces, thin films, buried layers and nano-structures. XPEEM image signals are contributed from photoelectrons, Auger electrons, backscattering electrons and secondary electrons excited by X-rays of certain energy. In this work, a Monte Carlo model for XPEEM image simulation is built. XPEEM images in total electron yield (TEY) mode are simulated with this model for several nanostructures (spheres and cylinders) of silver deposited on/in a silicon substrate (Ag/Si). The simulated XPEEM image in TEY mode for Ag dot array on a Si substrate is quite close to an experimental image. Furthermore, the XPEEM image simulation has been performed for different incident X-rays and for different geometric structures.     

Pulsed laser deposition of indium antimonide

Single crystalline oriented films of indium antimonide have been grown on cadmium telluride substrates by the pulsed laser deposition technique. The films were (111) oriented which is the substrate orientation. The composition of the grown films were found to deviate from that of the target owing to loss of antimony during evaporation. This deviation from stoichiometry led to film-substrate reaction, resulting in mixed interface. The antimony deficiency in the films were controlled by correcting the stoichiometry, which led to avoiding mixed interfaces. The stoichiometric films showed good surface morphology and well defined sharp interfaces. The IR transmission spectrum showed sharp band to band absorption and effective detection in the MWIR. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

X-ray topographic studies of cadmium selenide

The perfection of single crystal platelets of cadmium selenide, as grown from the vapour phase, has been investigated by X-ray projection topography. Individual dislocations, stacking faults, fringe patterns, curvature of the lattice planes, and the effects of precipitates, have been detected. Dislocations have been identified having Burgers vectors 1/31 1¯20 and 0 0 01 with screw, edge, mixed and 60° configurations.     

High pressure X-ray studies of polymers

A systematic study was made on polyethylene at high pressures and elevated temperatures using X-ray diffraction. Polyethylene with an initial chain-folded morphology and the orthorhombic crystal structure did not transform to any other phase before melting at the temperature and pressure used. Crystallization, however, at high pressures producing extended-chain crystals gave rise to either a new crystal phase, probably hexagonal, or the orthorhombic phase, depending on the crystallization conditions. A reversible solid-state phase transformation was observed between the orthorhombic and hexagonal phases. None of the previous interpretations put forward to account for the high pressure DTA and dilatometric studies of polyethylene, would appear to be appropriate in view of these findings.     

Surface and in depth chemistry of polycrystalline WO/sub 3/ thin films studied by X-ray and soft X-ray photoemission spectroscopies

The chemical composition of surface and underneath layers of WO/sub 3/ thin films, deposited by thermal evaporation and annealed in air at different temperatures, has been studied by means of soft X-ray and X-ray photoemission spectroscopies. Both the W 4f and valence band spectra have been analyzed. The analysis has been performed on samples as inserted and after an annealing process in an ultra high vacuum. The results have shown that the surface always presents a nonstoichiometric WO/sub 3/ compound, whose spectral components do not depend on the sample preparation. Instead, the study of the underneath layers has shown that the WO/sub 3/ films annealed in air at 500/spl deg/C are highly stoichiometric and stable, while the samples heated in air at 300/spl deg/C are much more sensitive to the vacuum thermal treatment showing the presence of reduced WO/sub x/ phases, whose intensity and chemical states change after the in vacuum annealing procedure.     

Electrical conductivity,thermoelectric power and optical absorption studies of amorphous and crystalline gallium antimonide thin films

Amorphous films (240–1740 Å thick) of gallium antimonide were formed by vacuum evaporation onto goldseal glass slides and onto sodium chloride crystals. They were annealed in successive cycles to obtain the ideal amorphous state. The heat treatment was continued until the crystalline phase was obtained. The electrical conductivity, the thermoelectric power with respect to bulk silver and the optical absorption were measured in all these films before and after crystallization. The electron diffraction patterns of the as-deposited, the annealed and the crystalline films were obtained using a transmission electron microscope. The activation energy for conduction ΔE, the amorphous-to-crystalline transition temperature, the density of states at the Fermi level N(_EF) and the optical energy gap E_o were evaluated.     

Studies of CaF2-CdSe interfaces using UV and X-ray photoemission spectroscopy and Auger electron spectroscopy

We investigated overlayers of CaF₂ deposited in ultrahigh vacuum onto CdSe surfaces using UV and X-ray photoemission spectroscopy and Auger electron spectroscopy. The interfaces exhibit very little reaction or interdiffusion and are remarkably abrupt. The results are compared with metal-CdSe interfaces and possible applications are discussed.