Intrinsic defects in GaAs and In GaAs through hybrid functional calculations

Hannu-Pekka Komsa, Alfredo Pasquarello
2012
Conference paper

Vacancies, antisites, and dangling bonds in GaAs and In0.5Ga0.5As are studied through hybrid density functionals. The As antisite is found to have a low formation energy in As-rich conditions and defect levels at mid-gap in correspondence of experimental defect densities at the GaAs/oxide and InGaAs/oxide interfaces. In n-type GaAs, the Ga vacancy also shows defect levels in agreement with measured defect densities and competitive formation energies. For both GaAs and InGaAs, the As dangling bonds are located near the valence band maximum. The Ga dangling bond in GaAs is found just below the conduction band-edge in correspondence of experimentally observed states, whereas its defect level is resonant with the conduction band in InGaAs. (C) 2011 Elsevier B.V. All rights reserved.

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Hannu-Pekka Komsa, Alfredo Pasquarello
2012
Conference paper

Abstract

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https://infoscience.epfl.ch/record/180295?ln=en

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Density functional theory

Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (

Hybrid functional

Hybrid functionals are a class of approximations to the exchange–correlation energy functional in density functional theory (DFT) that incorporate a portion of exact exchange from Hartree–Fock t

Dangling bond

In chemistry, a dangling bond is an unsatisfied valence on an immobilized atom. An atom with a dangling bond is also referred to as an immobilized free radical or an immobilized radical, a reference

Identification of defect levels at InxGa1-xAs/oxide interfaces through hybrid functionals

Hannu-Pekka Komsa, Alfredo Pasquarello

Hybrid density functional calculations and atomistic models are used to study point defects in III-V compounds. We first study dangling-bonds in InxGa1-xAs. In GaAs, the cation dangling-bond levels are found in the upper part of the band gap, but they are in resonance with the conduction band in In0.53Ga0.47 As and InAs. The As dangling-bond level falls within the band gap, at about 0.1 eV from the valence band maximum. Dangling bonds are thus identified as possible origin for the experimentally observed defect states near the band edges at InxGa1-xAs/oxide interfaces. To investigate the origin of the experimental defect density at mid gap, we then focus on GaAs and consider other native defects, such as the As antisite, the Ga vacancy, and the As vacancy. The assignment to the As antisite is favored by the correspondence of calculated and measured defect levels, its low formation energy, and the observed dependence of the defect density on As surface concentration. (C) 2011 Elsevier B.V. All rights reserved.

Elsevier2011

Charge transition levels of the Ge dangling bond defect at Ge/insulator interfaces

Audrius Alkauskas, Peter Broqvist, Alfredo Pasquarello

We calculate defect levels of dangling bonds in germanium using hybrid density functionals. To validate our approach, we first consider the dangling bond in silicon finding two well-separated defect levels, in excellent correspondence with their experimental location. Application of our scheme to the dangling bond in germanium then yields two very close defect levels lying just above the valence band, consistent with the location of the experimentally determined charge neutrality level. The small correlation energy and the proximity to the valence band edge provide an explanation for the absence of clear defect signatures in electrical and electron spin resonance experiments. Â© 2008 Elsevier Ltd. All rights reserved.

2008

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Defect levels of dangling bonds in silicon and germanium are determined within their respective band gaps through the use of hybrid density functionals. To validate our approach, we first considered the dangling bond in silicon finding two well-separated defect levels in excellent correspondence with their experimental location. Application to the dangling bond in germanium then yields two very close defect levels lying just above the valence band, which is consistent with the experimental location of the charge neutrality level. The occurrence of negative-U behavior leads to a reduced fraction of neutral dangling bonds, thereby suppressing the electron-spin-resonance activity.

2008