A Tracer Diffusion Study of Diverse Photo‐Ionic Phenomena in Strontium Titanate

Abstract By generating photo‐ionic phenomena, super‐bandgap illumination has opened up a new and promising avenue for modulating the thermodynamic and kinetic properties of compound semiconductors. In this study, three photo‐ionic phenomena—modifying a surface reaction rate, altering an ionic space‐charge layer, and changing bulk nonstoichiometry—are examined directly for the model system SrTiO _3−δ . ¹⁸ O ₂ / ¹⁶ O ₂ exchanges with and without UV illumination, with subsequent ion‐beam analysis, are employed to obtain as a function of temperature the respective, characteristic quantities: oxygen surface exchange coefficients , surface space‐charge potentials Φ ₀ , and bulk oxygen tracer diffusion coefficients . Two strong interfacial photo‐ionic effects are found: at T = 796 K, for example, UV illumination enhanced by a factor of 10 ^2.5 and lowered Φ ₀ by 25%. No significant change in is observed, placing bounds on the UV‐induced change of bulk nonstoichiometry δ. The enhancement of and the depression of Φ ₀ ( T ) are described with analytical models that include a temperature‐independent, UV‐generated increase in electron concentration. The enhancement of from UV illumination is found to be limited at lower temperatures by a parallel enhancement mechanism. This study thus resolves inconsistencies in reported photo‐ionic phenomena and furthermore provides a firm, quantitative foundation for future exploration.