Equilibrium Structure and Schottky Barriers at Eras/Gaas Interfaces
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ABSTRACT The equilibrium structures as well as the electronic Schottky barriers for (100) ErbiumArsenide/Gallium-Arsenide (ErAs/GaAs) arsenic and gallium terminated interfaces have been determined by ab-initio calculations using the local-density approximation and a full-potential linear-muffin-tin-orbital method. In both cases the arsenic sublattice was chosen to be continuous across the interface in accordance with experiments on Rutherford backscattering channeling. Band structures, densities of states, and charge density distributions were also determined for the interfaces. The comparison of the total supercell energies reveals that the gallium terminated (chain) interface is more energetically stable than the arsenic terminated (shadow) interface. It also shows that the equilibrium interface separation for the arsenic terminated interface corresponds to an ideal structure when arsenic forms undistorted face-centered cubic lattice. The separation in the gallium terminated interface is quite substantial and is 60% larger than that of the ideal situation. The model also predicts that no buckling of the ErAs interface monolayer will occur for either structure. The computed Schottky barriers for holes (after a semi-empirical quasiparticle self-energy correction) are 0.6 eV for the chain interface and 0.4 eV for the shadow interface. INTRODUCTION The epitaxial growth of Rare-Earth Pnictide (RE-V) materials on conventional III-V semiconductors has opened up a number of exciting possibilities for new devices. Metal-base transistors and resonant tunneling diodes are among the potential applications. These materials' magnetic behavior due to the open 4f shell of erbium may be harnessed for other novel devices. A theoretical understanding of these magnetic properties has suggested the possibility of magnetically tunable electrical devices or optically controlled magnetic storage. The development of any such device however depends upon properties of the interface at the heterojunction. Of particular interest is the height of the Schottky barrier. One of the peculiarities of the interface in question is that it is formed by materials with different crystal structures. Bulk erbium-arsenide forms a rock-salt lattice while gallium-arsenide is zincblende (ZB). Another interface distinction is that the atomic structure is not unique. That is, more than one continuous high-symmetry interface can form between erbium-arsenide and gallium arsenide. Rutherford backscattering (RBS) channeling studies [1, 2], however, reveal that the As sublattice at the interface is continuous. This leaves two distinct candidate structural models, which are illustrated in Fig. 1. vStructural relaxations of the rocksalt/zinc-blende {001} interfaces have been previously studied by Tarnov [3] for the closely related case of ErAs/AlAs. We follow his nomenclature for the interface models. The first one corresponds to to the gallium terminated surface of GaAs and is referred to as the chain model because of the occurence of Ga-As zigzag chains at the inte
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