Epitaxial growth and properties of thin film oxides

A method based on a controlled solid-solid reaction was used to fabricate heterostructures between single-walled carbon nanotubes (SWCNTs) and nanorods or particles of silicon carbide and transition metal carbides. Characterization by high-resolution transmission electron microscopy and electron diffraction indicates that the heterostructures have well-defined crystalline interfaces. The SWCNT/carbide interface, with a nanometer-scale area defined by the cross section of a SWCNT bundle or of a single nanotube, represents the smallest heterojunction that can be achieved using carbon nanotubes, and it can be expected to play an important role in the future fabrication of hybrid nanodevices.

https://science.sciencemag.org/content/sci/285/5434/1719.full.pdf

Heterostructures of Single-Walled Carbon Nanotubes and Carbide Nanorods

Ion beam synthesized polycrystalline semiconducting FeSi2 on Si(001) has been investigated by transmission measurements at temperatures between 10 and 300 K. The existence of a minimum direct band gap was demonstrated and its variation with the temperature was studied by means of a three‐parameter thermodynamic model and the Einstein model. Band tail states and states on a shallow impurity level were found to give rise to the absorption below the fundamental edge. The presence of an Urbach exponential edge was shown and the temperature dependence of the Urbach tail width was also studied based on the Einstein model. A strong structural disorder associated with grain boundaries between and within the FeSi2 grains and their related defects was found to be the dominant contribution at room temperature.

Optical absorption study of ion beam synthesized polycrystalline semiconducting FeSi2

Studies of the properties and characteristics of transition metal silicides have been stimulated by their (potential) use in integrated circuit technology. This review describes some of the most recent studies in this field of research. Formation mechanisms of silicides are discussed in some detail. A division is made between near-noble and refractory metal silicidation which aids in the understanding of differences in formation mechanisms of the various silicides. The evolution of the components of thin film stress during metal silicidation is also elucidated. In the review of the practical uses of these materials, emphasis is placed on specific processes involving laterally confined (self-aligned) silicide film formation as more advanced applications require film formation only in certain localized regions on a Si wafer.

https://iopscience.iop.org/article/10.1088/0034-4885/56/11/002/pdf

Transition metal silicides in silicon technology

Semiconducting silicide-silicon heterostructures : growth, properties and applications

Epitaxial thin films of the semiconducting transition metal silicide, beta‐FeSi2, were grown on (001) silicon wafers. The observed matching face relationship is FeSi2(100)/Si(001), with the azimuthal orientation being FeSi2[010]‖‖Si〈110〉. This heteroepitaxial relationship has a common unit mesh of 59 A2 area, with a mismatch of 2.1%. There is a strong tendency toward island formation within this heteroepitaxial system.

Epitaxial films of semiconducting FeSi2 on (001) silicon

Reflection high‐energy electron diffraction (RHEED) is an experimentally simple technique, and yet a powerful one for examining the structure of a substrate surface and for monitoring the surface crystal structure and the crystallographic orientation of thin films during their growth. However, it can be difficult to learn to interpret the RHEED patterns of new materials, because a practical and adequately detailed introduction to the technique is not generally available. To address this need, we develop the geometrical principles of RHEED; using the kinematic approximation, we show how a particular point of the sample surface’s reciprocal net gives rise to a diffraction maximum at a particular location on the RHEED viewing screen. We explain the origins of ‘‘reciprocal lattice rods,’’ RHEED streaks, and Laue rings. We show how to calculate the streak spacing, and clarify the basic effect on the RHEED pattern of using a nonzero angle of incidence for the incident beam. Crystalline nets, reciprocal nets, an...

A review of the geometrical fundamentals of reflection high‐energy electron diffraction with application to silicon surfaces

Semiconducting β‐FeSi2 is drawing much current research interest because of hoped‐for silicon‐based optoelectronics applications. The study of heteroepitaxial film growth on silicon depends heavily upon several transmission and reflection electron‐diffraction techniques. Because of the complicated crystal structure of this material, the possibility of competing heteroepitaxial relationships, the propensity for formation of epitaxial variants by rotation twinning, and the uncertainty in the crystalline surface nets, the analysis of experimental diffraction patterns is complicated. A theoretical reference for a number of fundamental electron‐diffraction patterns is provided and they are illustrated with a broad range of experimentally obtained patterns from the surfaces of epitaxial films. In situ transmission reflection high‐energy electron diffraction (RHEED) (transmission electron diffraction with conventional RHEED instrumentation), from rough but epitaxial films, is of great utility and quite feasible ...

Surface electron‐diffraction patterns of β‐FeSi2 films epitaxially grown on silicon

Epitaxially aligned films of β‐FeSi2 were grown on (001) silicon by reactive deposition epitaxy (RDE), molecular‐beam epitaxy (MBE), and solid‐phase epitaxy (SPE). Although the matching crystallographic faces, FeSi2 (100)/Si(001), remained invariant throughout this study, two different azimuthal orientations predominated, depending on the deposition mode and growth temperature. Films with the FeSi2[010]∥Si〈110〉 orientation (grown by RDE at typically 500 °C) were of a genuine large‐area single‐crystal structure; however, the surface morphology was rough due to islanding which always preceeded the formation of a continuous film. Films of the alternative azimuthal orientation FeSi2[010]∥Si〈100〉 (which were grown by SPE at typically 250 °C or by MBE at temperatures as low as 200 °C on top of an SPE‐grown template) have a much smoother surface morphology. However, there was some loss of purity in the epitaxial alignment at these extremely low temperatures. Excellent RHEED (reflection high‐energy electron diffr...

Robert G. Long

Papers

Epitaxial films of semiconducting FeSi2 on (001) silicon

A review of the geometrical fundamentals of reflection high‐energy electron diffraction with application to silicon surfaces

Surface electron‐diffraction patterns of β‐FeSi2 films epitaxially grown on silicon

Epitaxial orientation and morphology of β‐FeSi2 on (001) silicon

Optical and electrical properties of semiconducting rhenium disilicide thin films