Characterization and modulation of oxygen vacancy defects in metal/SrTiO_3-δ Schottky heterojunctions

Strontium titanate, SrTiO_3-δ (STO), can be made semiconducting and even metallic using high temperature anneals by introducing oxygen vacancy defects (δ > 0). Controlled thermal anneals with various temperatures and durations are employed to create specific defect profiles near the STO surfaces. Thermal sublimation or e-beam evaporation technique is then used to apply gold (Au) contact electrodes to the thermally treated STO substrates and create Schottky junctions. The presence of the oxygen vacancy defects strongly alters the electrical properties of these junctions as measured by transport, capacitance and low frequency noise. Our comparative study of these Schottky Au/STO junctions reveals that (i) the concentration of oxygen vacancy defects increases at the higher annealing temperature (ii) an improved spatial distribution/uniformity of defects is obtained by either lengthening the annealing duration or raising the annealing temperature. We show that the electrical characterizations of Schottky junction discussed here can serve as a useful tool to probe defects near the interfaces of novel materials and unravel information that is not easily accessed by other approaches.