Clemens J. Först

The interface between silicon and a high- k oxide

The ability of the semiconductor industry to continue scaling microelectronic devices to ever smaller dimensions (a trend known as Moores Law) is limited by quantum mechanical effects: as the thickness of conventional silicon dioxide (SiO2) gate insulators is reduced to just a few atomic layers, electrons can tunnel directly through the films. Continued device scaling will therefore probably require the replacement of the insulator with high-dielectric-constant (high-k) oxides, to increase its thickness, thus preventing tunnelling currents while retaining the electronic properties of an ultrathin SiO2 film. Ultimately, such insulators will require an atomically defined interface with silicon without an interfacial SiO2 layer for optimal performance. Following the first reports of epitaxial growth of AO and ABO3 compounds on silicon, the formation of an atomically abrupt crystalline interface between strontium titanate and silicon was demonstrated. However, the atomic structure proposed for this interface is questionable because it requires silicon atoms that have coordinations rarely found elsewhere in nature. Here we describe first-principles calculations of the formation of the interface between silicon and strontium titanate and its atomic structure. Our study shows that atomic control of the interfacial structure by altering the chemical environment can dramatically improve the electronic properties of the interface to meet technological requirements. The interface structure and its chemistry may provide guidance for the selection process of other high-k gate oxides and for controlling their growth.

Projector augmented wave method:ab initio molecular dynamics with full wave functions

A brief introduction to the projector augmented wave method is given and recent developments are reviewed. The projector augmented wave method is an all-electron method for efficient ab initio molecular dynamics simulations with full wave functions. It extends and combines the traditions of existing augmented wave methods and the pseudopotential approach. Without sacrificing efficiency, the PAW method avoids transferability problems of the pseudopotential approach and it has been valuable to predict properties that depend on the full wave functions.

Structural and electronic properties of the interface between the high-k oxide LaAlO3 and Si(001)

The structural and electronic properties of the LaAlO(3)/Si(001) interface are determined using state-of-the-art electronic structure calculations. The atomic structure differs from previous proposals, but is reminiscent of La adsorption structures on silicon. A phase diagram of the interface stability is calculated as a function of oxygen and Al chemical potentials. We find that an electronically saturated interface is obtained only if Al atoms substitute some of the interfacial Si atoms. These findings raise serious doubts whether LaAlO3 can be used as an epitaxial gate dielectric.

First-principles calculations of strontium on Si(001)

This paper reports state-of-the-art electronic structure calculations on the deposition of strontium on the technologically relevant, (001) orientated silicon surface. We identified the surface reconstructions from

Band alignment at the La2Hf2O7∕(001)Si interface

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Chemistry of La on the Si(001) surface from first principles

monolayers and relate them to experimentally reported data. A phase diagram is proposed. We predict phases at

Electronic Structure Methods: Augmented Waves, Pseudopotentials and The Projector Augmented Wave Method

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Heteroepitaxial growth of high-k gate oxides on silicon: insights from first-principles calculations on Zr on Si(0 0 1)

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