P.A. Redhead

Bio: P.A. Redhead is an academic researcher from National Research Council. The author has contributed to research in topics: Ion & Ionization. The author has an hindex of 9, co-authored 10 publications receiving 3319 citations.

Growth and applications of Group III-nitrides

Abstract: Recent research results pertaining to InN, GaN and AlN are reviewed, focusing on the different growth techniques of Group III-nitride crystals and epitaxial films, heterostructures and devices. The chemical and thermal stability of epitaxial nitride films is discussed in relation to the problems of deposition processes and the advantages for applications in high-power and high-temperature devices. The development of growth methods like metalorganic chemical vapour deposition and plasma-induced molecular beam epitaxy has resulted in remarkable improvements in the structural, optical and electrical properties. New developments in precursor chemistry, plasma-based nitrogen sources, substrates, the growth of nucleation layers and selective growth are covered. Deposition conditions and methods used to grow alloys for optical bandgap and lattice engineering are introduced. The review is concluded with a description of recent Group III-nitride semiconductor devices such as bright blue and white light-emitting diodes, the first blue-emitting laser, high-power transistors, and a discussion of further applications in surface acoustic wave devices and sensors.

Gas-assisted focused electron beam and ion beam processing and fabrication

Abstract: Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

Desorption from Metal Surfaces by Low‐Energy Electrons

Abstract: The effect of low‐energy (15–200‐eV) electrons on hydrogen, oxygen, carbon monoxide, and barium adsorbed on tungsten has been investigated by a field‐emission technique. Desorption cross sections σ were determined from work function and Fowler—Nordheim pre‐exponential changes and are significantly smaller than would be expected for comparable molecular processes. Marked variations in cross section with binding mode within a given system were found. Thus σH=3.5 10—20 cm2 and 5×10—21 cm2 for processes tentatively interpreted as the splitting of molecularly adsorbed H2 and desorption of H, respectively; σ0=4.5×10—19 cm2 for a loosely bound state and σ0≤2×10—21 cm2 for all other states; σBa<2×10—22 cm2 under all conditions. In the case of CO (reported in detail elsewhere), three binding modes observed previously could be confirmed and differentiated by their different cross sections: σvirgin=3×10—19 cm2; σβ=5.8×10—21 cm2, σα=3×10—18 cm2; conversion by electrons of virgin to β σvβ≥10—19 cm2. These results are interpreted in terms of transitions from the adsorbed ground state to repulsive portions of excited states, followed by de‐exciting transitions which prevent desorption. Arguments are made to show that the excitation cross sections should be essentially ``normal,'' i.e., ∼10—16 to 10—17 cm2, and that the much smaller over‐all cross sections observed are due to high transition probabilities to the ground state, estimated as 1014 to 1015 sec—1. A detailed calculation for the case of exponentially varying transition probabilities and repulsive upper states is presented and discussed, and the variations in cross section with binding mode made plausible. It is shown that low‐energy electron impact constitutes a sensitive tool for studying chemisorption.