Photoluminescence investigations of differently annealed and doped SrTiO3 single crystals in varying atmospheres

Strontium titanate is a well-known transition metal oxide for memory applications, which also exhibits interesting optical properties. Here, we utilized intrinsic and extrinsic doping of strontium titanate single crystals, e. g. oxygen vacancies, niobium and lanthanum. To introduce oxygen vacancies, SrTiO3 single crystals were vacuum-annealed. The existence of free charge carriers was controlled by means of infrared (IR) spectroscopy. A model to extract the electron density will be figured out. The determination of defect levels in the band gap related to surface and bulk oxygen vacancies was performed by photoluminescence (PL) measurements. The interaction between surface defects and atmosphere is highlighted by using different temperatures and gases. We found a time dependence of the photoluminescence intensity, which was attributed to oxygen incorporation at the surface during laser exposure. In addition, surface sensitive investigation methods like elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS) were used to clarify surface absorption effects under different ambient conditions. Implications for the situation at metal-oxide contacts will be presented.