The behaviour of donor-doped SrTiO3 surfaces under high-temperature treatment

Perovskites of ABO3 type like strontium titanate are of great practical concern as dielectric material or future material for oxygen sensors operating at high temperatures. Remarkable for this perovskite is its capability to incorporate a rather large amount of foreign elements and hereby change its electrical properties from insulating to n- or p-type semiconducting and even metallic behaviour. Annealing donor doped SrTiO3 (100), (111) and (111) single crystals under reducing or oxidizing conditions leads to the formation of islands or nanodots accompanied by a change of the stoichiometry of the surface and the near surface region. These alterations and the chemical composition of the secondary phases strongly depend on the experimental conditions like oxygen partial pressure (p(O2)), temperature, annealing duration, and dopant concentration. The annealed surfaces were observed by MIES and UPS to detect changes in the electronic structure, via XPS and AES to investigate the changes in the stoichiometry of the surfaces and the bulk and changes in the topography were investigated via AFM and STM. Using a defect chemistry model and thermodynamic calculations, I develop a consistent model explaining these observations both under reducing and oxidizing conditions