Reduction of SrTiO₃ Substrates by Pulsed Laser Deposition of Oxygen-Deficient Perovskite Films

SrTiO₃ (STO) is a common substrate material for the growth of many perovskite oxide thin films and heterostructures. Oxygen deficiency in STO induces metallic behavior in bulk and thin film form. In this presentation, we report on the metallicity of STO substrates induced by pulsed laser deposition (PLD) of STO films in various growth conditions. STO substrates annealed in the same growth conditions remain insulating. By varying background gas composition (O₂, N₂, Ar, 99%N₂/1%O₂) and pressure at a deposition temperature of 750°C, we find: (1) a strong dependence of the transport on O₂ partial pressure, transitioning from metallic to insulating behavior between ~7–10×10^-6 Torr; (2) increasing resistivity with increasing total pressure for fixed O₂ partial pressure; and (3) that metallic behavior persists to higher deposition pressures for N₂ and Ar compared to O₂. Samples with higher conductance exhibit a homogenously darker color. These results suggest that, during the PLD process, the deposition kinetics are a dominant factor in the formation of oxygen vacancies which then diffuse into the substrate. Understanding these mechanisms is crucial to prevent STO substrate reduction during PLD of films which require low O₂ partial pressures during growth.