NSLS-II Seminar

Before 1998, a crystalline oxide-silicon interface had been long sought for on account of its value for a number of applications. These applications range from gate oxides in field effect transistors to optical waveguides for electro-optical switching of information on optical fiber. While we have had some success in realizing such applications that mostly rely on bulk oxide properties, we have also uncovered technologically important science in the interface itself. This science is based on an interface phase that is a sequence of atomic layers deposited using molecular beam epitaxy. This sequence was invented by generalizing rules developed in the mid to late 1980’s for growing epitaxial metal superlattices. Importantly, the sequence satisfies thermodynamic equilibrium along a route that leads from the silicon (001) surface to a lattice-matched alkaline earth oxide. The five atomic layers of this sequence also define an interface phase that has two functional properties of its own. First, the physical structure of the interface sets up a dipole affecting oxide-silicon band offsets that can be tuned by changing interface composition. Finally, the electrical structure of the interface has the properties of a 2d semiconductor that can serve as a conducting channel at the quantum limit of scaling for the field effect transistor.