Graphite overlayers on SiC surfaces
In the new funding period the interaction of graphite layers on top of SiC surfaces is studied in addtion to the theory of doping. There are strong experimental indications that the graphite aggregates play a key role in the formation of Ohmic contacts on SiC. Ohmic contacts are an important preequisite for the manufacturing of p-n diodes. It was observed that with annealing temperatures above 1000ºC SiC/nickel contacts always show an Ohmic behaviour, although the pure nickel/SiC interface has a Schottky barrier. This significant and technologically important change in the behaviour was recently attributed to the catalytic formation of graphite inclusions at the interface. It is well known that under high temperatures the SiC(0001) surface evaporates silicon, so that thin graphite layers with hiqh quality form. It is the goal of this project to understand the interaction between the graphite layer and the underlying substrate. The structural properties are investigated as well as the electronic interface states by efficient ab initio methods. This information will support the development of Ohmic contacts on SiC as well as the interaction of graphite inclusions with SiC in general, which were recently proposed as nanowires buried within the SiC crystal.