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 Moore's Law(1)) 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(2), 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 ABO(3) compounds on silicon(3-7), the formation of an atomically abrupt crystalline interface between strontium titanate and silicon was demonstrated(8-10). 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.