J.K.N. Lindner

Origins of field enhancement in electron field emission from ion beam synthesized SiC layers

SiC layers were synthesized by high-dose carbon implantation into silicon. Their electron field emission properties were studied and correlated with results from atomic force microscopy (AFM) and conducting AFM measurements. It is clearly demonstrated that there are two types of field enhancement mechanisms responsible for the improvement of the electron field emission properties of these ion beam synthesized SiC layers. In the as-implanted samples, the local field enhancement effect is attributed to electrical inhomogeneity due to the existence of small conducting graphitic clusters embedded in the layer. On the other hand, in the annealed samples, the dominant field enhancement mechanism is attributed to a surface morphology effect due to the formation of small protrusion structures at the surface.

STRUCTURAL CHARACTERIZATION OF THE TEMPERATURE DEPENDENCE OF C60-THIN FILMS ON MICA (001) BY X-RAY DIFFRACTION

Thin C60 films have been deposited on mica(001) substrates by thermal evaporation at substrate temperatures between room temperature and 200 °C and at a constant deposition rate. The influence of the substrate temperature on the growth of C60‐thin films has been systematically investigated by x‐ray diffraction. θ–2θ measurements of the (111) peaks show a decrease of the full width at half‐maximum (FWHM) with increasing substrate temperature, leading to a minimum FWHM of 0.15° for a substrate temperature of 200 °C. Oriented films with an out‐of‐plane mosaic spread of Δω=0.2° could be grown at a substrate temperature of 150±25 °C. It can be shown that the in‐plane epitaxial arrangement C60(111)∥mica(001) is determined by the seeding conditions and is independent of the substrate temperature. An increasing substrate temperature enhances the epitaxial alignment of the C60 crystals oriented with a {111} face parallel to surface and also the azimuthal alignment of the twins which are rotated by 60° about the su...

Mechanisms in the ion beam synthesis of SiC layers in silicon

Abstract Single-crystalline buried 3C-SiC layers with rectangular carbon concentration profiles can be formed in silicon by ion beam synthesis using high-dose carbon implantation at constant or intentionally varied target temperatures and subsequent annealing at 1250°C. Layer formation during annealing starts from a box-shaped depth distribution of equally sized SiC nanocrystals present after implantation. In this paper, some of the mechanisms involved in the evolution of this precipitate depth distribution, including the nucleation, the growth and the ballistic destruction of precipitates as well as the carbon mediated amorphization induced by the release of high concentrations of carbon atoms from destroyed precipitates are described on the basis of cross-sectional TEM and high-resolution TEM investigations as well as Monte-Carlo simulations.

ION BEAM INDUCED AMORPHIZATION AND RECRYSTALLIZATION OF SI/SIC/SI LAYER SYSTEMS

Epitaxial, buried silicon carbide (SiC) layers have been fabricated in (100) and (111) silicon by ion beam synthesis (IBS). In order to study the ion beam induced epitaxial crystallization (IBIEC) of buried SiC layers, the resulting Si/SiC/Si layer systems were amorphized using 2 MeV Si2+ ion irradiation at 300 K. An unexpected high critical dose for the amorphization of the buried layers is observed. Buried, amorphous SiC layers were irradiated with 800 keV Si+ ions at 320 and 600°C, respectively, in order to achieve ion beam induced epitaxial crystallisation. It is demonstrated that IBIEC works well on buried layers and results in epitaxial recrystallization at considerably lower target temperatures than necessary for thermal annealing. The IBIEC process starts from both SiC/Si interfaces and may be accompanied by heterogenous nucleation of poly-SiC as well as interfacial layer-by-layer amorphization, depending on irradiation conditions. The structure of the recrystallized regions in dependence of dose, dose rate, temperature and crystal orientation is presented by means of TEM investigations.

Formation of buried epitaxial silicon carbide layers in silicon by ion beam synthesis

RBS/channeling, X-ray diffraction and transmission electron microscopy (TEM) as well as cross-sectional transmission electron microscopy (XTEM) are used to study the formation of well-defined, epitaxial 3C-SiC layers in Si(100) and Si(111) by high dose implantation of 180 keV C ions and subsequent thermal annealing at 1250 °C. The dose dependence of the carbon redistribution during the post-implantation anneal is studied in detail, revealing the possibility to grow well-defined substoichiometric and stoichiometric silicon carbide layers as well as 3C-SiC layers with a large concentration of excess carbon atoms. The presence of crystalline SiC nuclei in the as-implanted state and their depth distribution are shown to be important for the carbon redistribution into a discrete layer during annealing. XRD monitoring of the epitaxial 3C-SiC component formed during implantation indicates the build-up of lattice distortions close to the stoichiometry dose. After annealing, the approximately 170 nm thick continuous SiC layers are covered by 300 nm thick crystalline silicon top layers, containing individual SiC precipitates. Cross-sectional TEM investigations reveal sharp interfaces between Si and SiC layers and almost unstrained Si on top and underneath the layers. First results are reported indicating that SiC can be formed also in homogenous deep buried layers using MeV ion beam synthesis.

Formation and annealing of periodically arranged amorphous SiCx nanoclusters in silicon

Abstract The formation of a continuous amorphous layer upon high-dose carbon implantation into silicon at elevated temperatures is preceded by the formation of periodically arranged amorphous SiC x nanoclusters and lamellae. The dose and temperature dependence of their formation and the annealing behavior is studied after 180 keV C + implantations at temperatures of 150–350 °C and doses of 1– 9×10 17 C / cm 2 mainly by cross-sectional transmission electron microscopy (XTEM). Annealing of the nanoclusters at temperatures closely above the crystallization temperature of SiC is shown to result in the partial recrystallization of lamellae into chains of spherical SiC x nanoclusters and in the formation of cavities and crystalline inclusions. The observations are discussed on the basis of a simple model.

Investigation of the nucleation and growth of SiC nanostructures on Si

Using in situ reflection high energy electron diffraction (RHEED), ex situ atomic force microscopy (AFM) and transmission electron microscopy (TEM) the early stages of SiC growth on Si during the carbonisation were investigated in a solid source molecular beam epitaxy equipment. Different mechanisms of SiC precipitate growth by SSMBE were found. The SiC growth during carbonisation of Si(111) at 600°C is controlled by diffusion and at higher temperatures by a two-dimensional nucleation process, which is mononuclear at 660°C and polynuclear above 750°C. At temperatures greater than 750°C and 850°C three-dimensional nucleation occurs at (111) and (100) surfaces, respectively.

keV- and MeV- Ion Beam Synthesis of Buried SiC Layers in Silicon

Homogeneous, epitaxial buried layers of 3C-SiC have been formed in Si(100) and Si(111) by ion beam synthesis (IBS) using 180 keV high dose C ion implantation. It is shown that an annealing temperature of 1,250 C and annealing times of 5 to 10 h are sufficient to achieve well-defined Si/SiC/Si layer systems with abrupt interfaces. The influence of dose, annealing time and temperature on the layer formation is studied. The favorable dose is observed to be dependent on the substrate orientation. IBS using 0.8 MeV C ions resulted in a buried SiC precipitate layer of variable composition.

MeV ion beam synthesis of well-defined buried 3C-SiC layers in silicon

Well-defined, homogeneous, deep-buried 3C-SiC layers have been formed in silicon by ion beam synthesis using MeV C{sup +} ions. Layers are characterized by RBS/channeling, X-ray diffraction, x-sectional TEM and electron diffraction. The redistribution of implanted carbon atoms into a rectangular carbon depth distribution associated with a well-defined layer during the post-implantation anneal is shown to depend strongly on the existence of crystalline carbide precipitates in the as-implanted state.

MeV ion implantation induced damage in relaxed Si1−xGex

The damage produced by implanting, at room temperature, 3-μm-thick relaxed Si1−xGex alloys of high crystalline quality with 2 MeV Si+ ions has been studied as a function of Ge content (x=0.04, 0.13, 0.24, or 0.36) and Si dose in the dose range 1010–2×1015 cm−2. The accumulation of damage with increasing dose has been investigated by Rutherford backscattering spectrometry, optical reflectivity depth profiling, and transmission electron microscopy. An enhanced level of damage, and a strong decrease in the critical dose for the formation of a buried amorphous layer in Si1−xGex is observed with increasing x. Electron paramagnetic resonance studies show that the dominant defects produced by the implantation are Si and Ge dangling bonds in amorphouslike zones of structure similar to a-Si1−xGex films of the same x, and that the effect of increasing the ion dose is primarily to increase the volume fraction of material present in this form until a continuous amorphous layer is formed. A comparative study of the op...