S. McKernan

Direct observation of ordering in (GaIn) P

Ga x In 1 − x Pepilayers grown under a range of growth conditions by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates have been studied in the electron microscope. The results show the presence of an ordering of the group III sublattice parallel to some of the {111} planes. Dark-field images directly reveal ordered domains of different orientations that appear not to be perfect, but contain many planar defects parallel to the growth surface.

Ga0.5In0.5P/GaAs interfaces by organometallic vapor‐phase epitaxy

Organometallic vapor phase epitaxial growth of most III–V compounds is normally performed under group‐V‐rich conditions, making it difficult to form an abrupt interface during a change of group V species. The Ga0.5In0.5P/GaAs interface is of interest because it offers a potential advantage over AlGaAs/GaAs selectively doped structures by reducing the deep‐level donor problem. In this communication, formation of the Ga0.5In0.5P/GaAs interface during low‐pressure organometallic vapor phase epitaxial growth is studied by comparing a series of three superlattices grown using different interface formation techniques. Continuous growth, growth stop under group V gas, and growth stop followed by a purge of all reactants are analyzed by Raman scattering, transmission electron microscopy (TEM), and 4‐K photoluminescence. All superlattices show good TEM contrast between layers. The growth stop is found to reduce both P and In intermixing into the GaAs layers, relative to the continuously grown superlattice. The pur...

A quantitative analysis of strong-beam α fringes from {110} antiphase boundaries in GaAs

Abstract The reliability of a quantitative comparison of contrast between experimental and simulated strong-beam transmission electron microscope images depends on an accurate determination of a number of parameters. It is shown that, by recording simultaneous bright-field and dark-field images, the main sources of uncertainty in such an analysis, namely the crystal potential and the absorption parameter, can be reduced substantially. This technique has been employed in order to determine the rigid-body translation across {110} antiphase boundaries in GaAs, by analysis of strong-beam α fringes.

Direct observation of grain orientation in YBa2 Cu3 O7-δ thin films

Abstract Using a recently developed specimen-preparation technique to examine heteroepitactic growth in ceramics, the early development of grain orientation in thin YBa2 Cu3 O7-δ films prepared by pulsed-laser ablation can be determined. The technique involves deposition directly on to a specially prepared electron-transparent substrate. The films are examined during the early stages of growth by transmission electron microscopy. Three different orientations corresponding to different alignments of the c axis of the YBa2 Cu3 O7-delta; unit cell with the MgO substrate could be determined from the particle morphology in the image, but were not detected by selected-area diffraction due to their small size.

Characterization of APBs in GaAs Grown on Si and Ge

Antiphase boundaries are observed in epilayers of GaAs grown by organometallic vapor phase epitaxy on Ge substrates and are then invariably found to show a tendency to facet. Stacking-fault-like fringes caused by the translation of adjacent grains give the information on the relative displacement of the two grains at these interfaces and show that this translation does not have a fixed magnitude for a particular interface but varies with the orientation of the interface. Preferred orientations of the antiphase boundaries and the rigid-body translations have been studied using transmission electron microscopy. Interactions between antiphase boundaries and interfaces have been examined here in heterolayer structures consisting of alternating layers of GaAs and Al x Ga l−x As grown on an (001) Ge substrate. The possibility of using atomic-resolution imaging to investigate the atomic structure of APBs is illustrated and the images are compared with those predicted by image simulation.

On the Structure of Planar Defects in ALN

Aluminum nitride has a great potential as a semiconductor substrate material. However, the defects which occur in this material are very detrimental to the material properties. ‘Domelike’ or ‘D’ defects, consisting of a flat basal fault joined to a curved planar fault, are examined by TEM. They are shown to be inversion domains, using a newly developed technique for polarity determination in the TEM. Structural models are proposed for the defects which incorporate a layer of alumina one unit cell thick into the basal fault of the defect.

Observation of double ribbons in GaAs and AlGaAs

Abstract Stacking-fault double-ribbons have been observed in GaAs; a compound semiconductor. Values for the extrinsic and intrinsic stacking-fault energies of 41·2±5 mJm−2 and 46·5±6 mJm−2, respectively, were obtained from the widths of the stacking-fault ribbons. The ratio of the intrinsic to extrinsic stacking-fault energy is found to be 1·13±0·08.

The observation of stacking-fault tetrahedra in III-V compounds

Abstract The first observations of stacking-fault tetrahedra in ion-implanted III-V compounds are reported. The structure and orientation of the stacking-fault tetrahedra are briefly described. The tetrahedra are present in the near-surface region that recrystallized during the annealing. High-resolution images suggest that the stacking-fault tetrahedra are of the vacancy type.

Growth and Microstructure of Aluminum Nitride Thin Films

The synthesis of aluminum nitride thin films by pulsed-laser ablation is demonstrated. The films were formed on single-crystal sapphire and graphite substrates. A number of techniques were used to characterize the films: transmission and scanning electron microscopy, Rutherford backscattering spectrometry and x-ray diffraction.

The growth of hematite by oxidation of iron-bearing olivine

Abstract The controlled oxidation of iron-bearing olivine has been performed by the repeated annealing and re-examination of thin TEM specimens. With an annealing temperature of ≈900°C, particles of hematite are formed on the surface, leaving an iron-depleted olivine. Thin olivine TEM specimens with a [010] foil normal produce hematite islands with an orientation relationship determined by (100) 0 ‖(0001) h :[001] 0 ‖[10 1 0] h or (100) 0 ‖(0001) h :[001] 0 ‖[ 1 010] h . The hematite particles show strong faceting parallel to the {0001}, {10 1 0} and {10 1 2: planes and, with prolonged annealing, may grow together to produce twin boundaries which are parallel to {0001} or {10 1 0} planes. Neglecting the small lattice mismatch, the “close-packed” planes are continuous across all of these interfaces.