Band offsets at semiconductor-oxide interfaces from hybrid density-functional calculations

Band offsets at semiconductor-oxide interfaces are determined through a scheme based on hybrid density functionals, which incorporate a fraction alpha of Hartree-Fock exchange. For each bulk component, the fraction alpha is tuned to reproduce the experimental band gap, and the conduction and valence band edges are then located with respect to a reference level. The lineup of the bulk reference levels is determined through an interface calculation, and shown to be almost independent of the fraction alpha. Application of this scheme to the Si-SiO2, SiC-SiO2, and Si-HfO2 interfaces yields excellent agreement with experiment.

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Audrius Alkauskas, Peter Broqvist, Fabien Devynck, Alfredo Pasquarello
2008
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https://infoscience.epfl.ch/record/141789?ln=en

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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

Density functional theory

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Band gap

In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band st

Charge transition levels of carbon-, oxygen-, and hydrogen-related defects at the SiC/SiO2 interface through hybrid functionals

Audrius Alkauskas, Peter Broqvist, Fabien Devynck, Alfredo Pasquarello

We calculate charge transition levels of various defects at the SiC/SiO2 interface within a scheme based on hybrid density functionals, which accurately reproduce the involved band gaps and band offsets. The defect levels are first evaluated in bulk models of the interface components and then aligned with respect to the interface band diagram through the use of a model interface showing good structural and electronic properties. Interface-specific polarization effects are evaluated separately through classical electrostatics. We considered carbon-related defects involving single atoms and dimers in both the crystalline SiC substrate and the amorphous SiO2 oxide. Our investigation also comprises oxygen-and hydrogen-related defects, including the Si-Si bond (O vacancy), the Si-2-C-O structure, the peroxy linkage, and the hydrogen bridge (Si-H-Si). Among the defects studied, the Si-2-C-O structure represents the best candidate for the high defect density measured near the conduction band of SiC.

2011

Defect levels of dangling bonds in silicon and germanium through hybrid functionals

Audrius Alkauskas, Peter Broqvist, Alfredo Pasquarello

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

Effect of improved band-gap description in density functional theory on defect energy levels in alpha-quartz

Audrius Alkauskas, Alfredo Pasquarello

We compare defect energy levels of point defects in alpha-quartz using density functionals of different accuracy: a standard generalized-gradient-approximation functional and a hybrid functional. The latter is known to improve the description of band gaps through the incorporation of a fraction of Hartree-Fock exchange. The separations between the defect levels are found to be preserved when going from the standard to the more accurate hybrid functional, indicating that they are already well described with the standard functional. We also find that the defect wave functions obtained with the two functionals are very similar. Consequently, the defect energy levels pertaining to the hybrid functional can be obtained through the perturbational method. (C) 2007 Elsevier B.V. All rights reserved.

2007