Feliciano Giustino

Atomistic models of the Si(100)–SiO2 interface: structural, electronic and dielectric properties

We review the structural, electronic and dielectric properties of atomistic models of the Si(100)-SiO2 interface, which have been purposely designed in order to match a large variety of atomic-scale experimental data. After describing the generation procedure and the structural properties of two specific interface models, we study the corresponding electronic structure and dielectric response within the framework of density-functional theory. Particular emphasis is given to a systematic comparison between the atormstic properties of our model interfaces and experiment. Besides. synthesizing the present status of our experimental knowledge on the Si(100)-SiO2 interface, these models provide a solid and necessary basis for future investigations in the area of gate stacks for Si-based microelectronics.

Modeling of Si 2p core-level shifts at Si-(ZrO2)(x)(SiO2)(1-x) interfaces

We model Si 2p core-level shifts at Si–(ZrO2)x(SiO2)1−x interfaces for varying Zr content x. Using a first-principles approach, we calculate Si 2p shifts for a model interface and for cluster models, and establish the validity of a linear dependence of these shifts on both the number of second-neighbor Zr atoms and the O coordination of these Zr atoms. Applying this relation to model structures of amorphous Zr silicates generated by classical molecular dynamics, we find that the Si 2p line shifts to lower binding energies with increasing Zr content x, in accord with experimental data.

Atomistic model of the 4H(0001)SiC-SiO2 interface: structural and electronic properties

Through the sequential use of classical molecular dynamics and first‐principles relaxation methods, we generate an abrupt model interface for the 4H(0001)SiC‐SiO2 interface showing regular structural parameters without any coordination defect. The valence and conduction band offsets are calculated and found to be in fair agreement with the experimental values. Si‐2p core‐level shifts are calculated for this model interface and compared with available experimental data.

DIELECTRIC AND INFRARED PROPERTIES OF ULTRATHIN SiO2 LAYERS ON Si(100)

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 infrared properties of atomically thin SiO2 layers on Si(100) through a fully quantum-mechanical description. For this purpose, we construct atomistic models of the Si(100)-SiO2 interface on the basis of available experimental data, by using both classical and first-pninciples simulation methods. Our model structures account for the experimental density of coordination defects, the distribution of partially oxidized Si atoms, the oxide mass density profile, and the lateral displacements of the Si atoms in the channel region. Our first principles calculations indicate that the permittivity of the SiO2 layer departs from the bulk value in the limit of atomically thin oxides. This departure is well described through the consideration of an interfacial suboxide layer with a thickness of about 0.5 nm and a dielectric constant of about 6-7. As a consequence, the equivalent oxide thickness of the interfacial layer is smaller than the corresponding physical thickness by 0.2-0.3 nm. Variations of the local dielectric screening occur on length scales corresponding to first-neighbor distances, indicating that the dielectric transition is governed by the chemical grading. We find that the enhanced ionic screening in the substoichiometric oxide results from Si-O bonds formed by Si atoms in the partial oxidation state Si+2. We also extend our investigation to the infrared absorption at the Si(100)-SiO2 interface. Our study allows us to shed light on the pronounced thickness-dependent red shift of the oxygen stretching modes, which has so far not found a definite interpretation. Indeed, our calculations clearly show that the red shift results from a softening of the Si-O stretching vibrations in the interfacial layer.

Atomic-scale modelling of the Si(100)-SiO2 interface

We discuss the structural, electronic and dielectric properties of a model structure of the Si(100)‐SiO2 interface that accounts for the amorphous nature of the oxide. After showing that the structural properties of this model are consistent with a variety of experimental data, we consider the variation of the valence and conduction band edges across the interface. Our calculations indicate that the width of the electronic structure transition from the substrate to the oxide is 0.7–0.8 nm. We also address the dielectric properties based on an atomic‐scale approach, and provide estimates for the effective dielectric constants of the substrate, the suboxide, and the stoichiometric oxide regions.

Atomic-scale investigation of the dielectric screening at the interface between silicon and its oxide

We investigate the dielectric screening across the Si-SiO 2 interface using a first-principle approach. By determining the profile of the microscopic polarization and the effective polarizabilities of SiO n ( n = 0,‥4) structural units, we show that the variation of the local screening across the interface relates to the chemical grading. The oxide region near the Si substrate shows the same dielectric permittivity as bulk SiO 2 as long as the oxide is locally stoichiometric. The suboxide region carries an enhanced permittivity, with a value intermediate between those corresponding to bulk Si and SiO 2 . The implications of these findings for the scalability of the equivalent oxide thickness in high- κ gate stacks are discussed.