Publications de Alfredo Pasquarello

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Using a density functional approach, we study structural and electronic properties of the 4H(0001)-SiC/SiO2 interface. Through the sequential use of classical and ab initio simulation methods, we generate an abrupt model structure which describes the transition between crystalline SiC and amorphous SiO2 without showing any coordination defect. The first step in our generation procedure consists in identifying suitable interfacial bonding patterns which account for the bond density reduction across the inter

Using density functional calculations, we study a set of candidate defects for Fermi-level pinning at GaAs/oxide interfaces. The set of considered defects comprises both bulklike and interfacial defects, including As antisites, Ga and As dangling bonds, th ...

The band alignment and the chemical bonding at the beta -Ga2O3/AlN and beta -Ga2O3/GaN interfaces are studied through hybrid functional calculations. We construct realistic slab models with III-O (III = Al, Ga) bonds dominating the chemical bonding at both ...

In and Ga impurities substitutional to Al in the oxide layer resulting from diffusion out of the substrate are identified as candidates for electron traps under inversion at In0.53Ga0.47As/Al2O3 interfaces. Through density-functional calculations, these de ...

First-principles molecular dynamics simulations are carried out to study the structural properties of liquid GeSe2. We use a generalized gradient approximation for the exchange and correlation energy, which we find to improve significantly upon the local density approximation in describing both the short- and the intermediate-range structure. A very good agreement with experiment is obtained for the total neutron structure factor over the entire range of momentum transfer. In particular, the first sharp dif

We study the electronic structure and the dielectric permittivity of ultrathin oxide layers on Si(I 00) substrates. By considering two different Si(l 00)-SiO2 interface models, we first show that the electronic structure in the interfacial oxide differs from the corresponding bulk counterpart due to silicon-induced gap states. Then, we calculate the permittivity of the first few angstroms of the oxide within a density-functional approach. For sub-nanometric oxides, we find that the oxide permittivity increa

Using a first-principles approach, we study the vibrational properties of vitreous SiO2 which are measured in neutron-scattering experiments. We adopt a model structure consisting of corner-sharing tetrahedra, which was previously generated using first-principles molecular dynamics. We calculate the dynamic, structure function S(q,E) as a function of wave vector q and energy E by taking explicitly into account the correlations between different atoms as given by the normal modes. The effects of temperature

We study the interfacial electronic properties of a model Si-SiO2-Si structure which is intended to simulate the substrate-oxide-polysilicon stack in metal-oxide-semiconductor devices. The structural properties of this model are shown to match closely those of the real system, as determined by a number of atomic-scale experimental probes. In particular, the model introduced here takes into account the disordered reconstruction at the Si-SiO2 interface, and the amorphous nature of the 2 nm thick oxide. For t

Using hybrid density functional theory, we address point defects susceptible to cause charge compensation upon Mg doping of GaN. We determine the free energy of formation of the nitrogen vacancy and of several Mg-related defects. The entropic contribution ...

We present a first-principles investigation of the structural properties of two models for the Si(001)-SiO2 interface. The models derive from attaching tridymite, a crystalline form of SiO2, to Si(001), and then allowing for full relaxation. These models do not show electronic states in the silicon gap, as required by electrical experiments. They contain the three intermediate oxidation states of silicon, consistent with photoemission experiments. We study bond length and bond angle distributions and measur

Calculations of formation energies and charge transition levels of defects routinely rely on density functional theory (DFT) for describing the electronic structure. Since bulk band gaps of semiconductors and insulators are not well described in semilocal ...

We study the nature of excess electrons in CsPbBr3 and identify several single and double polaronic states. We emphasize the importance of proper inclusion of the self-interaction corrections for the stability of small electron polarons in this material. W ...

A first-principles investigation of Si 2p core-level shifts at the Si(001)-SiO2 interface is presented. We introduce several relaxed interface models obtained by attaching different crystalline forms of SiO2 to Si(001). These model structures contain the minimal transition region required to accommodate the three intermediate oxidation states of silicon, in accord with photoemission experiments. The bond density mismatch is fixed by saturating all the bonds, as required by electrical measurements, Calculate

Through the use of the piecewise-linearity condition of the total energy, we correct the self-interaction for the study of polarons by constructing nonempirical functionals at the semilocal level of theory. We consider two functionals, the gamma DFT and mu ...

The defect levels of the nitrogen dangling bond at the Si/SiO2 interface are determined through a density-functional approach. The composition grading at the interface is modeled through crystalline and amorphous models of stoichiometric SiO2, nitrided SiO ...

The accuracy of nonscreened and screened hybrid functionals for the calculation of defect levels within the band gap is assessed for the As antisite in GaAs, the nature of which is well characterized experimentally. A set of functionals differing by the fr ...

We develop a scheme for finite-size corrections of vertical transition energies and single-particle energy levels involving defect states with built-in ionic polarization in supercell calculations. The method accounts on an equal footing for the screening ...

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/GaAs heterojunctions are emerging as promising candidates for next-generation power electronics, photonics, and energy devices, leveraging the high breakdown voltage and thermal stability of Ga

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alongside the mature technology, high hole mobility, and higher refractive index of GaAs. The efficiency of these devices depends strongly on the band alignment between the two materials, however both type-I and type-II alignment have been reported in the literature for these heterostructures. To

The requirement for increasingly thin (

In this work, we systematically evaluate the accuracy in band gap prediction of range-separated hybrid functionals on a large set of semiconducting and insulating materials and carry out comparisons with the performance of their global counterparts. We obs ...

Alfredo Pasquarello

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Structural and electronic properties of an abrupt 4H-SiC(0001)/SiO2 interface model: Classical molecular dynamics simulations and density functional calculations

Fermi-level pinning through defects at GaAs/oxide interfaces: A density functional study

Band alignment at beta-Ga2O3/III-N (III = Al, Ga) interfaces through hybrid functional calculations

Nature of electron trap states under inversion at In0.53Ga0.47As/Al2O3 interfaces

Short- and intermediate-range structure of liquid GeSe2

Electronic and dielectric properties of a suboxide interlayer at the silicon-oxide interface in MOS devices

Dynamic structure factor of vitreous silica from first principles: Comparison to neutron-inelastic-scattering experiments

Electronic structure at realistic Si(100)-SiO2 interfaces

Self-compensation due to point defects in Mg-doped GaN

Structurally relaxed models of the Si(001)-SiO2 interface

Band-edge problem in the theoretical determination of defect energy levels: The O vacancy in ZnO as a benchmark case

Small Electron Polarons in CsPbBr3: Competition between Electron Localization and Delocalization

Theory of Si 2p core-level shifts at the Si(001)-SiO2 interface

Nonempirical semilocal density functionals for correcting the self-interaction of polaronic states

Charge transition levels of nitrogen dangling bonds at Si/SiO2 interfaces: A first-principles study

Assessing the accuracy of hybrid functionals in the determination of defect levels: Application to the As antisite in GaAs

Finite-size corrections of defect energy levels involving ionic polarization

The impact of interfacial chemistry on the band offset of GaAs/Ga2⁢O3 heterostructures

Interface structure between silicon and its oxide by first-principles molecular dynamics

Range-separated hybrid functionals for accurate prediction of band gaps of extended systems