D. J. H. Cockayne

Damage to epitaxial GaN layers by silicon implantation

Ion channeling and cross‐sectional transmission electron microscopy were used to study the extent and nature of Si ion implantation damage in epitaxial GaN layers at liquid nitrogen temperature. Results indicate that displacement damage produced by the implantation undergoes substantial dynamic annealing during implantation. As a result, at moderate implantation doses residual implantation damage consists of a dense network of secondary defects, such as clusters and loops, which are a consequence of incomplete annihilation of implantation‐produced defects. Amorphous layers can be produced, but the doses required are extremely high (≳1016 cm−2) and amorphization appears to ‘‘nucleate’’ at the surface.

Ion damage buildup and amorphization processes in AlxGa1-xAs

The nature of keV ion damage buildup and amorphization in AlxGa1−xAs at liquid‐nitrogen temperature is investigated for various Al compositions using Rutherford backscattering channeling, transmission electron microscopy, and in situ time‐resolved‐reflectivity techniques. Two distinct damage buildup processes are observed in AlxGa1−xAs depending on Al content. At low Al content, the behavior is similar to GaAs whereby collisional disorder is ‘‘frozen in’’ and amorphization proceeds with increasing dose via the overlap of damage cascades and small amorphous zones created by individual ion tracks. However, some dynamic annealing occurs during implantation in AlGaAs and this effect is accentuated with increasing Al content. For high Al content, crystallinity is retained at moderate ion damage with disorder building up in the form of stacking faults, planar, and other extended defects. In the latter case, amorphization is nucleation limited and proceeds abruptly when the level of crystalline disorder exceeds ...

An approach to quantitative compositional profiling at near-atomic resolution using high-angle annular dark field imaging

Abstract The compositional profile of a GaAs Al 0.6 Ga 0.4 As interface is investigated through analysis of a high resolution high-angle annular dark field image. Image calculations are carried out using a multislice code that incorporates thermal diffuse scattering, and an algorithm is developed for quantitative matching between these images and the experimental image. The resulting compositional profile (with monolayer spatial resolution) is compared with an analogous quantitative chemical mapping experiment. The extension of this new technique to high resolution compositional mapping (in two dimensions) is briefly explored.

Misfit dislocations and critical thickness in InGaAs/GaAs heterostructure systems

The onset of misfit dislocation generation is investigated and the critical thickness is determined by transmission electron microscopy using the epitaxial lift‐off technique for InGaAs/GaAs single heterostructures and single quantum wells. The observed geometries of the dislocations in both cases are in good agreement with the predicted models [J. Appl. Phys. 41, 3800 (1970) and J. Cryst. Growth 27, 118 (1974)]. However, each dislocation undergoes the predicted elongation mechanism [J. Appl. Phys. 41, 3800 (1970)] at different strained‐layer thicknesses. A comparison of the predicted and the experimental critical thicknesses is given.

Analysis of films prepared by plasma polymerization of acetylene in a D.C. magnetron

Abstract The complex dielectric constant of amorphous hydrogenated carbon films was determined by reflection and transmission measurements in the photon energy range from 0.5 to 6.54 eV. The results, determined by the application of a sum rule, showed the presence of 0.47 π-bonded electrons per carbon atom in the films. Electron energy loss spectroscopy was carried out which confirmed the presence of π-bonded electrons and gave a value of the combined σ and π plasmon peak at 23 eV, too low to be consistent with the presence of a distinct phase containing diamond microcrystals or random tetrahedral bonding. A model is presented in which threefold coordinated sheets are linked by tetrahedrally bonded carbon atoms.

Novel impurity-free interdiffusion in GaAs/AlGaAs quantum wells by anodization and rapid thermal annealing

A novel impurity-free interdiffusion technique utilizing pulsed anodization and subsequent rapid thermal annealing at temperatures near 900 °C was reported. Enhanced interdiffusion was observed in the presence of an anodized GaAs capping layer in GaAs/AlGaAs quantum well structures. Transmission electron microscopy studies show evidence of interdiffusion. Photoluminescence spectra from interdiffused samples show large blue shift and no significant linewidth broadening. Possible mechanism of interdiffusion was discussed.

The structure and properties of ion‐beam‐synthesized boron nitride films

Films containing boron and nitrogen were prepared by electron‐beam evaporation of boron and bombardment of the growing film with nitrogen ions of energy up to 1500 eV. Hard films of high transparency (extinction coefficient <0.01) were prepared with nitrogen‐to‐boron atomic arrival ratios greater than one. The optical constants in the visible part of the spectrum were determined as a function of B‐to‐N atomic ratio in the film and substrate temperature using optical photometry. Measurements of the optical constants were extended to 40 eV using a Kramers–Kronig analysis of electron‐energy‐loss spectra. Boron‐to‐nitrogen atomic arrival rates were determined and show that as ion energy and substrate temperature are increased ion flux must be increased to achieve the same stoichiometry. Film structure was imaged using high‐resolution electron microscopy, and the radial distribution function (RDF) was determined. The RDF of stoichiometric films showed that high substrate temperatures increased the size of the ...

Surface relaxation of strained heterostructures revealed by Bragg line splitting in LACBED patterns

Abstract Bragg line splitting near the shadow image of a thin strained InGaAs layer, buried in GaAs and without strain relief by misfit dislocations, was found in large angle convergent beam electron diffraction (LACBED) patterns of cross-section specimens. The surface relaxation of the built-in strain and the Bragg line intensities were calculated. A qualitative agreement between the experimental Bragg line splitting and the theoretical calculations is demonstrated Closer matching was achieved using a “line-force” model of the surface relaxation, whereas a Fourier transform solution showed significant underestimation of the Bragg line splitting. The possibility of characterising the built-in strain in thin strained layers, by measuring this Bragg line splitting in LACBED patterns, has been explored.

Electron optical techniques for microstructural andcompositional analysis of thin films

Abstract Electron optical methods of determining the atomic level microstructure ofthin films are discussed with reference to examples. The use of energy filtered electron diffraction and electron energy loss spectroscopy (EELS) are illustrated by using them to distinguish between amorphous carbons prepared by vacuum evaporation and the material prepared by condensing the carbon plasma stream from a vacuum arc. The latter is shown to consist almost entirely of tetrahedrally bonded carbon. These electron optical techniques are also applied to hexagonal and cubic boron nitride and to silicon and germanium carbides. Other techniques discussed are high resolution electron imaging and Kramers-Kronig analysis of EELS spectra.

Critical thickness determination in In x Ga 1-x As/GaAs strained-layer system by transmission electron microscopy

The critical thicknesses of InxGa1-xAs/GaAs and GaAs/InxGa1-xAs/GaAs strained-layer systems were determined by transmission electron microscopy using the lift-off technique. The onset of misfit dislocation generation has been observed for the first time and the geometries of the misfit dislocations in both uncapped and capped layers correspond to the predicted models. A comparison is given between the predicted and experimental critical thicknesses.