Abstract
For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect ${\mathrm{Ga}}_{As}$ is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as ${\mathrm{B}}_{As}$. This systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.
Highlights
A comprehensive and detailed understanding of the possible defects and their chemistry—formation energies, diffusion activation energies, defect energy levels—is necessary for quantitatively predictive modeling of processing and radiation effects in semiconductors such as GaAs [1,2]
First-principles electronic structure simulations are crucial to elucidating this defect physics, because, while some of the requisite atomic scale physics is available through experimental measurement [3,4], much is experimentally inaccessible or unknown, and can only be discovered and characterized through firstprinciples calculations [5]
Grown from a very Ga-rich melt, greater than ∼0.53 Ga mole fraction, the resistivity is instead p type, accompanied by the appearance of a shallow double acceptor, with levels at 78 and 203 meV above the valence band edge (VBE) [8,9,10]. This shallow double acceptor grows into the native undoped GaAs using liquid encapsulated Czochralski (LEC), liquid phase epitaxy (LPE), or vertical gradient freeze (VGF) technologies [8,11]
Summary
A comprehensive and detailed understanding of the possible defects and their chemistry—formation energies, diffusion activation energies, defect energy levels—is necessary for quantitatively predictive modeling of processing and radiation effects in semiconductors such as GaAs [1,2]. Grown from a very Ga-rich melt, greater than ∼0.53 Ga mole fraction, the resistivity is instead p type, accompanied by the appearance of a shallow double acceptor, with levels at 78 and 203 meV above the VBE [8,9,10]. The neutral gallium antisite, with two fewer electrons than the arsenic atom it replaces, introduces two holes into the bond network This can capture two electrons, and GaAs is expected to be a double acceptor. The involvement of boron in the defect, isovalent with gallium, would create a double acceptor, and could not be totally excluded, but Elliott et al [8,10] noted a lack of correlation between boron content and the acceptor concentration From these observations—as grown Ga-rich, likely intrinsic, tetrahedral symmetry, double acceptor—the natural inference was the shallow double acceptor was associated with the Ga antisite
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