In situ studies of the growth and oxidation of complex metal oxides by pulsed laser deposition

Abstract Pulsed Laser Deposition (PLD) is a versatile deposition technique for complex metal oxide thin films and heterostructures. Without sophisticated parameter engineering, a stoichiometric transfer between target and substrate can take place in a large pressure range of different gas ambient. As a result, PLD is widely applied in many research laboratories.However, the basic processes during PLD growth are not well understood. Therefore most of the research groups only carry out parameter optimization for PLD empirically. Although the thin film properties can be enhanced by empirical optimization of growth parameters, the exact correlation between PLD growth process and thin film property is hardly known. A better understanding in the correlation between PLD growth and thin film properties is gaining arising attention with its increasing importance for different complex metal oxide based electronics nowadays. The aspects to be investigated are different in various material systems. The first example is the Resistive Random Access Memories (ReRAM) based on complex metal oxides, e.g. SrTiO3 (STO) thin films, where the defects like cation vacancies in thin oxide films play a crucial role for the switching behavior. Only by understanding the defect formation process during the PLD process a rational design of defects in the thin film could be possible. The in-situ studies on the defect formation process during STO thin film growth are thus necessary. The second example is the conductive interface between two band insulators, e.g. LaAlO3 (LAO) and STO. Since its discovery one decade ago, the formation process of the conductive interface is not well understood. To understand the physical mechanism behind the conductive interface formation, it is of pivotal importance to learn when the formation takes place. Furthermore, the conductivity of LAO/STO heterostructures are significantly influenced by the defects like oxygen vacancies, which can be incorporated/eliminated both by growth and post-annealing process. So the in-situ study on the conductive interface formation and the study on the oxygen vacancy incorporation/elimination process during the growth and annealing process are needed. In this work the in-situ study on the defect formation process during STO homoepitaxy is carried out. The cation non-stoichiometries in STO thin films are introduced by the preferential scattering process during laser plume propagation. STO thin films with cation non-stoichiometry remains at the early growth stage within 2D growth mode. The defects are in this growth stage point defects inhibiting surface diffusion through surface strain. The cation non-stoichiometry leads further to the formation of extended defects as growth proceeds and the growth mode is changed. As an example, the Sr rich STO exhibits firstly 2D growth with subsequent surface termination change from TiO2 to SrO at low film thickness, whereas the further growth establishes anti-phase boundaries and lead to 3D island growth. The conductive interface formation process between LAO and STO is studied in-situ and real-time with Oblique Incidence Reflectance Difference technique (OIRD). In addition, the incorporation and elimination processes of oxygen vacancies in LAO/STO heterostructures are investigated as well. It is observed from the growth process that the first 3 unit cells (u.c.) LAO differ from the rest of LAO unit cells, indicating the electronic transfer happens at 3 u.c. and does not influence the first 3 u.c. LAO. The incorporation of oxygen vacancies into the STO takes place during the PLD growth of LAO, while the elimination of oxygen vacancies in STO is optimal at the growth temperature and pressure. The main reason for the incorporation of oxygen vacancies in STO is the impinging particles with high kinetic energy