I. V. Ivonin

Determination of the fractal dimension for the epitaxial n-GaAs surface in the local limit

Atomic-force microscopy studies of epitaxial n-GaAs surfaces prepared to deposit barrier contacts showed that major relief for such surfaces is characterized by a roughness within 3–15 nm, although “surges” up to 30–70 nm are observed. Using three independent methods for determining the spatial dimension of the surface, based on the fractal analysis for the surface (triangulation method), its section contours in the horizontal plane, and the vertical section (surface profile), it was shown that the active surface for epitaxial n-GaAs obeys all main features of behavior for fractal Brownian surfaces and, in the local approximation, can be characterized by the fractal dimension Df slightly differing for various measuring scales. The most accurate triangulation method showed that the fractal dimensions for the studied surface of epitaxial n-GaAs for measurement scales from 0.692 to 0.0186 μm are in the range Df = 2.490−2.664. The real surface area Sreal for n-GaAs epitaxial layers was estimated using a graphical method in the approximation δ → 0 δ is the measurement scale parameter). It was shown that the real surface area for epitaxial n-GaAs can significantly (ten times and more) exceed the area of the visible contact window.

The role of stress distribution at the film/barrier interface in formation of copper silicides

Silicide formation in thin Cu films subjected to thermal annealing has been investigated by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. It is shown that the periodic stress distribution at the film/barrier interface under elevated temperatures can govern the character of copper silicide formation. The effect of barrier layer material and substrate orientation on the distribution density and shape of Cu3Si crystallites has been studied.

Decomposition of a supersaturated solid solution of Fe in GaAs

The decomposition of a solid solution of iron in gallium arsenide at 900°C has been studied by magnetic force microscopy and transmission electron microscopy. The results demonstrate that annealing of Fe-doped GaAs for 3 h leads to the formation of disk-shaped ferromagnetic inclusions 50–500 nm in diameter and 1.5–50 nm in thickness. The average inclusion concentration is 1011 cm−3. The estimated decomposition time of the solid solution at 900°C is within 1 h.

A study of the process of decomposition of supersaturated GaAs:Fe solid solution by scanning probe microscopy

Using an atomic-force microscope, the decomposition of the supersaturated solid solution of iron-doped GaAs (GaAs:Fe) is studied. GaAs:Fe samples were obtained in the course of high-temperature diffusion of Fe into GaAs and subsequent annealing at a temperature by 200°C below the doping temperature. The measurements are performed for transverse cleavages along the cleavage planes of the GaAs:Fe wafers. It is shown that, during annealing of the GaAs:Fe samples, the supersaturated alloy decomposes with the formation of particles of the second phase from ∼50 nm to ∼1 μm in size. The particles of the second phase possess ferromagnetic properties at room temperature.

Effect of the growth temperature on the statistical parameters of GaN surface morphology

It is shown that it is necessary to find the scaling function for a more comprehensive analysis of the statistical parameters of the surface morphology of solids and, in particular, GaN epitaxial films. This function accounts for both the experimental parameters and the conditions of study. It is demonstrated by the example of an atomic-force microscopic study of gallium-nitride epitaxial films obtained at various temperatures that the scaling function makes it possible to relate in a single equation the following three parameters: the growth temperature, the scan length, and the number of measurement points. The function makes it possible to more precisely estimate the surface roughness in scanning regions larger than 10 × 10 μm and prognosticate its value upon a variation in the growth temperature.

Theoretical and experimental studies of surface processes in the course of molecular-beam epitaxy of gallium nitride

The method of atomic-force microscopy has been used to experimentally study the effect of growth conditions on the structure of the surface of epitaxial GaN layers grown by molecular-beam epitaxy. Quantitative values of the density, height, and width of growth centers in relation to the conditions of epitaxy are obtained; the average length of the diffusion path of particles limiting the GaN growth rate have been estimated; and the activation energies and the surface-diffusion coefficients for these particles have been calculated. The equilibrium composition of adsorbed layers at the GaN (0001) surface in a wide range of deposition temperatures and pressures of gallium and nitrogen has been calculated with account taken of the following components: gallium atoms, nitrogen atoms, and NH molecules. On the basis of the comparison of experimental data on the structure of the GaN surface with results of calculations concerning the composition of adsorbed layers on the growth surface, it was assumed that the growth of GaN layers is limited by supply of gallium.

Formation of a transition layer during heteroepitaxy of III–V compound semiconductors in gas-phase epitaxy systems

It is known that during gas-phase epitaxy of InP and GaAs the region of the film close to the heteroboundary is formed with altered phase, structural, and electrophysical properties. The main cause for this is formation of a transition layer due to a change in the growth mechanism (transition from nucleational to layer-step growth) and the structure of the growing surface (height and density of growth steps).

Electron microscope investigation of the morphology of the etched surface of gallium arsenide

An investigation was made of the micromorphology of the surface of GaAs single crystals produced by sulfuric acid etching. The observed acicular structure is highly stable to the reagents used to remove oxides and metals from the GaAs surface (HF, Trilon B, etc.) but can be removed mechanically. It is shown that the microstructure parameters depend on the ratio of the etchant components and the dopant level of the specimen. It is assumed that the distribution of the structural elements (columns) reflects the nature of the distribution of the alloying dopant in the crystal. Adsorption processes are taken to be responsible for column formation on the surface.

Fractal mode of distribution of surface potential of gate layer in gallium arsenide structure of field-effect transistor

On account of fractal nature (Df=2.62) of the gate layer of FET, instrumental characteristics, when length and width of the gate are reduced, will change disproportionally to square of change of linear dimensions of the gate (versus two-dimensional case) and noticeably slower - in proportion to changing of linear dimensions to the power of 4-Df, where 2<;;Df<;;3. The fractal nature of the surface potential of the gate layer might be caused by either fractal distribution of ionized donor impurity in the bulk and at its surface or by fractal distribution of charged adsorbing ions.

Influence of the Substrate Orientation on the Silicon Capture into A- and B- Sublattices of Gallium Arsenide in Molecular Beam Epitaxy

The influence of crystallographic orientation of the growth surface near (100) and (111)A GaAs singular faces on the silicon capture into A- and B-sublattices of gallium arsenide in molecular beam epitaxy is investigated by the electrophysical and photoluminescence methods. It is demonstrated that the silicon dopand is incorporated into GaAs layers not only as simple SiGa donors but also as elemental SiGa acceptors and more complex defects, namely, SiAs–VAs complexes. The concentration of defects of different types in layers depends on the orientation of the growth surface, and the amphoteric properties of silicon on the (111)A face are manifested stronger than those on the (100) face.