First principles analysis on interaction between vacancy near surface and dimer structure of silicon crystal

We investigated the interactions between the dimer structures in a reconstructed Si (100) surface and a vacancy to understand the behavior of the point defects near the surface using first principles calculations. The calculated results showed that even a vacancy set in the ninth layer from the surface affects the charges around the dimers. This effect intensifies if the vacancy moves to the surface. Similar to the vacancies in a bulk, Jahn-Teller distortion occurred at atoms around the vacancy. When the introduced vacancy approaches to the fourth layer from the bottom, this distortion increased, and thus decreases the total energy. The third layer, in which forming a vacancy requires the highest energy, becomes a singularity layer in a Si (100) surface with dimer structures. The model, in which a vacancy was introduced into the fifth layer from the surface, came to have a vacancy in the fourth layer as an optimized structure due to a Si atom moving from the fourth to the fifth layer. We can see a clear interaction between the vacancy-originated charges and the surface dimer-originated one in this movement. As a consequence, the nature of the interaction between a surface dimer and a vacancy is intermediated by their accompanying charges.