Electrical conductivity in oxygen-substituted SrTiO3-δ films

Enhancement of electrical conductivity in fundamentally insulating ABO3 perovskite oxide ferroelectrics is crucial for innovative applications in resistive switching, photovoltaics, and catalysis. One of the methods to raise conductivity in bulk crystals or ceramics relies on the possibility to remove and/or substitute oxygen atoms. Here, we explored this approach for thin films of the representative perovskite oxide SrTiO3. Small-signal AC conductivity was investigated in epitaxial and polycrystalline films, where oxygen vacancies (VO), nitrogen (N), or hydrogen (H) were introduced in situ during film growth. Hopping mechanism of conductivity was evidenced by the observed strong growth of AC conductivity with temperature, frequency, and AC voltage in all films. Small polarons were identified as charge carriers. Oxygen vacancies/substitutions were suggested to facilitate hopping probability by generating sites for carrier localization. Important ferroelectric devices were proposed to benefit from the revealed hopping conductivity owing to its unique increase with an electric field.