L. Dobos

Ion beam synthesis of graphite and diamond in silicon carbide

A high dose of 1×1018 cm−2, 60 keV carbon ions was implanted into single crystalline 6H silicon carbide (SiC) at elevated temperatures. The formation of carbon phases in the crystalline SiC lattice was investigated by cross sectional transmission electron microscopy. An amorphous, carbon rich phase was produced at 300 °C. Precipitates of graphite were obtained at 600 °C, whereas at 900 °C small diamond grains were produced. These grains are in perfect epitaxial relation with the surrounding SiC lattice.

Thermal decomposition of bulk and heteroepitaxial (100) InP surfaces: A combined in situ scanning electron microscopy and mass spectrometric study

The thermal decomposition of bulk and heteroepitaxial (100) InP surfaces is studied by in situ scanning electron microscopy combined with mass spectrometry. The onset of P evaporation coincides with the In droplet nucleation at about 480 °C and the major evaporation of phosphorous commences above 510 °C and corresponds to the serious deterioration of the surface. There is no significant difference between bulk and defected (heteroepitaxial InP/GaAs) samples. The relevance to InP technology is discussed.

Fractal behaviour of the surface of in situ heat treated metal-InP contacts

Abstract The heat treatment of metallised compound semiconductors results material diffusion and evaporation, called volatile component loss. In situ SEM and mass spectrometric study showed, that surface pattern has fractal character at heat treatment temperatures, where the volatile component loss has maximum value. The so-called fractal dimension or scaling factor of self-similarity ( D ) was evaluated for Au/InP ( D =1.57±0.01), Pd/InP ( D =1.75±0.01) and Au/Pd/InP contacts. The comparison of SEI and BEI images suggested that the geometrical surface patterns, resulted by the balling-up phenomenon, and the pattern, which possible describes the phase inhomogeneity on the same contact, can be characterised by different values of the fractal dimension. In the case of the studied Au/Pd/InP contact, D was 1.56±0.02 for balling up and D was 1.84±0.01 for phase distribution.

Properties of CrSi2 nanocrystallites grown in a silicon matrix

Semiconducting CrSi2 nanocrystallites (NCs) were grown by reactive deposition epitaxy. The NCs were covered by 100 nm of epitaxial silicon. Their structure, morphology and optical properties were investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet photoelectron spectroscopy (UPS) and optical reflectance spectroscopy (ORS). The preservation of the CrSi2 phase has been justified by UPS, by ORS, and by TEM measurements. The distribution of Cr was investigated by Rutherford backscattering (RBS). The electrically active defects were investigated by deep level transient spectroscopy (DLTS). The crystal structure of the NCs nucleated near the deposition depth is identified by high-resolution TEM as hexagonal CrSi2. Energy filtered TEM shows that most of the Cr is localized in the three-dimensional (3D) NCs. RBS shows that the concentration of Cr is appropriate for the deposited quantity. In the 0.1 nm Cr sample most of the Cr is localized near the surface; in the 0.6 nm Cr sample the concentration increases at the depth of Cr deposition, while in the 1.5 nm Cr sample the excess Cr is localized near the deposition depth. DLTS Arrhenius plots give activation energies of the defects appropriate for Cr contamination, however these defects may be related to the CrSi2 NCs.

Morphological investigation of the electrochemically etched GaAs (001) surface

In this paper, we investigate pattern formation on GaAs (001) surface after electrochemical layer removal by different aqueous HCl based electrolytes. Under polishing (non-selective) etching conditions the surface morphology displayed fractal behaviour. The morphological investigation of the surface was carried out using digital processing of scanning electron microscope images. The patterns were segmented by the so called grade of membership technique. Fractal properties were established using the box counting method.

Thermal decomposition of InP surfaces : volatile component loss, morphological changes, and pattern formation

The thermal decomposition of bulk and heteroepitaxial InP surfaces is studied by in-situ scanning electron microscopy combined with mass spectrometry and atomic force microscopy. Correlation is established between the evaporation of phosphorous and the formation of thermal etch pits. The formation of the pattern that the In droplets constitute is analysed using fractal mathematics. Only negligible roughening is induced by annealing outside the pits.

The Volatile Component Loss and the Surface Morphology of the Gold-Palladium Metallizations to the Compound Semiconductor Structures

Palladium based metal systems can be used to make ohmic contacts to A III B V compound semiconductors. A covering layer of gold is advantageous even from the point of view of bonding. Gold, palladium, Au/Pd layers were studied on InP and GaAs substrates. The samples were annealed in the vacuum chamber of the scanning electron microscope (SEM) and the volatile component losses (arsenic or phosphorus) were monitored by a quadrupole mass spectrometer. The changes of the surface morphology were studied using the SEM images. In the case of Pd/A III B V samples a single characteristic peak due to the interaction taking place between the palladium and the substrate was observed on the volatile component loss vs. temperature curve. In the case of Au/Pd/A III B v samples a second peak appeared on the evaporation vs. temperature curve due to the interaction between gold and A III B V substrate. The temperature of that second peak is about 50–60°C higher than in the case of a single gold layer on A III B V substrates because gold had to diffuse through the palladium layer, what hindered the reaction of gold with A III B V materials.

Heat treatment parameters effecting the fractal dimensions of AuGe metallization on GaAs

Correlation was detected between the thermal treatment parameters of the AuGe–GaAs system and surface fractal structure. Structural entropic calculations were used to confirm the results obtained by fractal calculations.

Selective electrochemical profiling of threading defects in mismatched heteroepitaxial systems

The defect structure of molecular beam epitaxy grown InGaAs/GaAs(001) heteroepitaxial systems is studied by using selective electrochemical etching. The InAs mole fraction varied between 0.03 and 0.3 whilst the layer thickness changed between 0.02 and 0.5 μm (above the critical layer thickness). Different aqueous electrolytes and bias voltages were applied to achieve optimum etching conditions. By incremental layer removal, the depth profile of the dislocation density was mapped. The density of defects is inversely proportional to the layer thickness and increases with misfit. The experimental results are compared to theoretical models.

Selective Electrochemical Profiling of Threading Dislocations in Mismatched InGaAs/GaAs Heteroepitaxial Systems

The defect structure in relaxed (100) InGaAs/GaAs heteroepitaxial systems grown by molecular beam epitaxy is studied by selective electrochemical (anodic) etching. By incremental layer removal, we map the depth profile of the dislocation density. The density of dislocations is inversely proportional to the layer thickness and increases with misfit. The results are compared to theoretical models.