Browsing by Author "Yang, L. H."
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Item Open Access Electronic and magnetic properties of zinc blende half-metal superlattices(A I P Publishing LLC, 2004) Fong, C. Y.; Qian, M. C.; Pask, J. E.; Yang, L. H.; Dag, S.Zinc blende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. We explore layered materials, consisting of alternating layers of zinc blende half-metals, by first principles calculations, and find that superlattices of (CrAs)1(MnAs)1 and (CrAs)2(MnAs)2 are half-metallic with magnetic moments of 7.0mB and 14.0mB per unit cell, respectively. We discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. We explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form.Item Open Access Model study of a surfactant on the GaAs(100) surface(Elsevier, 2002-11-01) Consorte, C. D.; Fong, C. Y.; Watson, M. D.; Yang, L. H.; Çıracı, SalimBased on the facts that: (a) the transverse acoustic vibrational branch frequency is softened at the Brillouin zone boundaries of crystalline GaAs; (b) at the surface, the Ga-As bond is stronger than Ga-Te bond; and (c) the requirement that the final bond orientation of the Te surfactant should be rotated by 90degrees with respect to its initial orientation, we carried out a model study of an exchange process in epitaxial growth of GaAs (100). Even with very restrictive conditions imposed on the atomic movements, this study explains why Te is an effective surfactant for this type of growth. (C) 2002 Elsevier Science B.V. All rights reserved.Item Open Access Reaction path for Te during surfactant-mediated epitaxial growth of GaAs (100)(American Physical Society, 2001) Consorte, C. D.; Fong, C. Y.; Watson, M. D.; Yang, L. H.; Çıracı, SalimUsing first-principles calculations and experimental evidence concerning the essential environment for surfactant-mediated epitaxial growth on the GaAs/Te~100! surface, we determine a short-ranged reaction path for the As↔Te exchange that is energetically favorable and prepares the surface for continued layer-by-layer growth. Furthermore, we explain the required partial coverage of the surfactant atoms as well as the required presence of both As and Ga adatoms.Item Open Access Spin-polarized ballistic transport in a thin superlattice of zinc blende half-metallic compounds(The American Physical Society, 2005) Qian, M. C.; Fong, C. Y.; Pickett, W. E.; Pask, J. E.; Yang, L. H.; Dag, S.We examine theoretically ballistic conduction in thin layers of zinc blende half metals, considering as an example a superlattice consisting of monolayers of GaAs and MnAs, a bilayer of CrAs, and a bilayer of GaAs. By artificially separating bilayers, we show that surface states thwart half metallicity. However, capping the metal-As bilayers restores half metallicity, and ballistic conduction of electrons within ∼0.3 eV of the Fermi level will give nearly 100% spin-polarized transmission in the direction of the superlattice. Recent developments suggest atomic layer epitaxy can be used to produce such thin layers for spintronic applications.Item Open Access Surfactant-mediated growth of semiconductor materials(Institute of Physics Publishing, 2002) Fong, C. Y.; Watson, M. D.; Yang, L. H.; Çıracı, SalimDuring epitaxial growth of semiconducting materials using either molecular beam epitaxy or organometallic vapour deposition, the addition of a surfactant can enhance two-dimensional layer-by-layer growth. This modified growth process is now called the surfactant-mediated growth (SMG) method. It has had an important impact on the development of technologically important materials in device applications, such as heterostructures used for laser applications. Recent developments that use surfactants to improve doping profiles in semiconducting systems and antisurfactants (ASMG) to grow quantum dots further ensure that SMG/ASMG will play a major role in the future development of optoelectronic materials and nanoparticles. In this paper, we review important earlier experimental work involving the SMG method as well as some recent developments. Theoretical work involving first-principles methods and kinetic Monte Carlo simulations are discussed but confined only to the surfactant effect.