Optical identification of oxygen vacancy formation at SrTiO3–(Ba,Sr)TiO3 heterostructures

We used molecular beam epitaxy (MBE) growth to control the density of oxygen vacancy-related (VO-R) defects at (Ba,Sr)TiO3/SrTiO3 heterojunctions along with depth-resolved cathodoluminescence spectroscopy (DRCLS), surface photovoltage spectroscopy and positron annihilation spectroscopy (PAS) to identify their optical signature, energy levels and spatial distribution. We grew (Ba,Sr)TiO3 epilayers on SrTiO3 using oxygen plasma-assisted MBE under a range of oxygen pressures and temperatures designed to control oxygen extraction from the SrTiO3 substrate that feeds the (Ba,Sr)TiO3 epilayer growth and generates oxygen vacancies. DRCLS and PAS identify a 2.95 eV optical emission with VO-R defect—valence band transitions that peak below the heterointerface and their interplay with 1.8 and 2.3 eV cation vacancies versus growth conditions. These studies reveal that native defects accumulate near SrTiO3/(Ba,Sr)TiO3 interfaces and are sensitive to growth conditions. (paper)