Home

Person

Alfredo Pasquarello

About
Privacy
Disclaimer

Graph Chatbot

Related publications (226)

Semiconductor defects at the 4H-SiC(0001)/SiO2 interface

We study several semiconductor defects at the 4H-SiC(0 0 0 1)/SiO2 interface within a spin-polarized generalized-gradient density-functional approach for identifying candidate defects responsible for the high density of interface defects measured in the up ...

2007

Structural properties of amorphous GeSe2

Alfredo Pasquarello

By using first-principles molecular dynamics within density functional theory, we study the structural properties of amorphous GeSe2 at T = 300 K. The amorphous configurations have been obtained via cooling from the liquid state followed by extensive relax ...

2007

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

Alfredo Pasquarello, Audrius Alkauskas

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 ...

2007

Hydrogen in Si(100)-SiO2-HfO2 gate stacks: Relevant charge states and their location

Alfredo Pasquarello, Peter Broqvist

Using a density functional approach, we study the energetics of various charged hydrogen states in the Si(100)-SiO2-HfO2 gate stack. We describe the SiO2-HfO2 transition region through model structures of amorphous hafnium silicate HfxSi1-xO2 with differen ...

AIP American Institute of Physics2007

Alignment of hydrogen-related defect levels at the Si-SiO2 interface

Alfredo Pasquarello, Audrius Alkauskas

We propose a method within density functional theory for aligning defect energy levels at interfaces without relying on experimental data. We apply our scheme to the alignment of charge transition levels of the interstitial hydrogen and the hydrogen bridge ...

2007

Migration of oxygen vacancy in HfO2 and across the HfO2/SiO2 interface: A first-principles investigation

Alfredo Pasquarello, Peter Broqvist

Oxygen vacancy migration is studied in monoclinic HfO2 and across its interface with SiO2 through density functional calculations. In HfO2, long-range diffusion shows activation barriers of 2.4 and 0.7 eV for the neutral and doubly positively charged vacan ...

AIP American Institute of Physics2007

Microscopic origin of concentration fluctuations over intermediate range distances in network-forming disordered systems

Alfredo Pasquarello

Ab initio molecular dynamics simulations of liquid GeSe2 show that the first sharp diffraction peak in the concentration-concentration structure factor S-CC(k) is due to a sequence of connected fourfold rings. These subunits can be viewed as chains of edge ...

2007

Proton-induced fixed positive charge at the Si(100)-SiO2 interface

Alfredo Pasquarello

Positively charged defects induced by protons at the Si(100)-SiO2 interface are studied through density-functional calculations and realistic interface models. Protons generally preserve the bonding network, but cause the spontaneous breaking of strained b ...

2007

Proton Diffusion in Amorphous SiO2 and Hafnium Silicate by Ab Initio Molecular Dynamics

Alfredo Pasquarello

We study proton diffusion in amorphous SiO2 and hafnium silicates at the atomic scale. In amorphous SiO2, ab initio molecular dynamics suggest that the dominant atomic process consists in cross-ring interoxygen hopping assisted by network vibrations. In ha ...

American Institute of Physics2007

First principles investigation of defects at interfaces between silicon and amorphous high-kappa oxides

Alfredo Pasquarello, Peter Broqvist

Experimental characterization is facing severe difficulties in elucidating the nature of defects at interfaces between silicon and amorphous high-kappa oxides. This motivates recourse to first principle simulation approaches based on density functional the ...

2007

Hyper-Raman spectrum of vitreous silica from first principles

Alfredo Pasquarello

We introduce a scheme for the calculation of nonresonant hyper-Raman spectra of vitreous materials within a density-functional formulation. Hyper-Raman tensors are obtained through the application of finite electric fields and explicitly account for the no ...

2007

First-principles investigation of the structural and vibrational properties of vitreous GeSe2

Alfredo Pasquarello, Luigi Giacomazzi

Using a density-functional scheme, we study the structural and vibrational properties of vitreous germanium diselenide (v-GeSe2). Through the use of classical and first-principles molecular-dynamics methods, we generate a set of structural models showing a ...

2007

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

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist

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 trans ...

2007

Vibrational spectra of vitreous germania from first-principles

Alfredo Pasquarello, Luigi Giacomazzi

We report on a first-principles investigation of the structural and vibrational properties of vitreous germania (v-GeO2). Our work focuses on a periodic model structure of 168 atoms, but three smaller models are also studied for comparison. We first carry ...

2006

Origin of fine structure in Si 2p photoelectron spectra at silicon surfaces and interfaces

Alfredo Pasquarello, Oleg Yazyev

Using a first-principles approach, we investigate the origin of the fine structure in Si 2p photoelectron spectra at the Si(100)-(2x1) surface and at the Si(100)-SiO2 interface. Calculated and measured shifts show very good agreement for both systems. By u ...

2006

Ion scattering simulations of the Si(100)-SiO2 interface

Alfredo Pasquarello, Angelo Bongiorno

We carry out ion scattering simulations to investigate the nature of the transition region at the Si(100)-SiO2 interface. Ion scattering experiments performed in the channeling geometry provide us with a genuine interfacial property, the excess Si yield, r ...

2006

Comment on "fraction of boroxol rings in vitreous boron oxide from a first-principles analysis of Raman and NMR spectra" - Umari and Pasquarello reply

Alfredo Pasquarello

2006

Dielectric and infrared properties of ultrathin SiO2 layers on Si(100)

Alfredo Pasquarello

The occurrence of an ultrathin SiO2 oxide layer at the interface between silicon and high-k dielectrics in metal-oxide-semiconductor devices contributes to degrading the capacitance of the gate stack. In this work, we investigate the dielectric and infrare ...

2006

Mixed Wannier-Bloch functions for electrons and phonons in periodic systems

Alfredo Pasquarello

We introduce mixed Wannier-Bloch functions for studying electronic and vibrational spectra of periodic systems. These functions carry both spatial localization and limited spectral broadening, thereby combining the advantages of descriptions based on energ ...

2006

Oxygen vacancy in monoclinic HfO2: A consistent interpretation of trap assisted conduction, direct electron injection, and optical absorption experiments

Alfredo Pasquarello, Peter Broqvist

The authors calculate energy levels associated with the oxygen vacancy in monoclinic HfO2 using a hybrid density functional which accurately reproduces the experimental band gap. The most stable charge states are obtained for varying Fermi level in the HfO ...

AIP American Institute of Physics2006

Page 10 of 12