First-Principles Study of Epitaxial Growth of Zinc-Blende CrAs on GaAs Substrates
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JJ3.8.1
First-Principles Study of Epitaxial Growth of Zinc-Blende CrAs on GaAs Substrates Kiichiro Mukose, Koichi Kusakabe and Naoshi Suzuki Graduate School of Engineering Science, Osaka University, Machikaneyama-cho 1-3, Toyonaka, Osaka 560-8531, Japan. ABSTRACT We study the epitaxial growth mechanisms of the zinc-blende CrAs on the GaAs substrates theoretically, from the first principles using the pseudopotential method. We assume some model structures containing various numbers of Cr adatoms or CrAs films on the GaAs (001) substrates, and compare the structural stabilities of them. We found that Cr adatoms may make some interstitial defects in the GaAs substrate in low coverage, but they can create a complete Cr layer in high coverage. INTRODUCTION Although the crystal structure of bulk CrAs is MnP type in thermal equilibrium, the zinc-blende type CrAs has been theoretically designed and predicted to be half-metallic, and a thin film of this new material on the GaAs substrates has been reported to grow experimentally by the molecular beam epitaxy (MBE) method [1]. This thin film shows ferromagnetic behavior at room temperature. Furthermore, zinc-blende GaAs/CrAs multilayers also have grown [2]. However, the thicknesses of the zinc-blende CrAs films and layers in these experiments are very thin, up to a few monolayers (ML). And the MBE growth conditions (the substrate temperature, the beam equivalent pressure etc.) can be chosen empirically, but cannot be determined theoretically. So far, theoretical studies for the growth mechanisms of this material are very few. We study theoretically the microscopic mechanisms of the epitaxial growth of this new material by the first-principles calculations, using the pseudopotential method. In this paper, we investigate stabilities of several patterns of surface structures, which contain various numbers of Cr adatoms, or CrAs thin films on the GaAs (001) substrate, to discuss the stabilities of the MBE growth process.
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COMPUTATIONAL DETALS We calculate electronic structures and evaluate total energies of surface structures, assuming several patterns of model structures containing Cr adatoms or CrAs films on the GaAs (001) substrates, using slab models. The each model structure is constructed with 5 ML slabs and 14.3 Å vacuum layers. The lattice-constant of deep layers of the substrate is fixed to be 5.73 Å as calculated for bulk GaAs. The adatoms and films are added on the both sides of the slabs. We have used ultra-soft pseudopotentials and plane-wave basis in our band calculations, with the “PWscf” code [3], which is a package of programs of the band calculations in the density functional theory (DFT). We have generated the ultra-soft pseudopotentials using the David Vanderbilt’s code [4] for Ga, As and Cr. For all calculations, we have used Perdew-Bruke-Ernzerhof’s form of the exchange-correlation interactions in the generalized gradient approximation (GGA) [5]. The plane-wave cut-off energy is chosen to be 25 Ry. The k-points are sampled from (4 × 2 × 1) grid fo
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