Persistent illumination-induced changes in polycrystalline TiO2 majority carrier concentration

Abstract

In polycrystalline semiconductors for which grain boundaries mediate a persistent change in majority carrier concentration on super-bandgap photostimulation, the change generally involves an increase. Capacitance–voltage measurements on thin-film polycrystalline anatase TiO2 demonstrate a photostimulated increase or decrease in majority carrier concentration, depending on film thickness. With the help of photoreflectance measurements, the results are interpreted in terms of deep-gap energy states that reside near grain boundaries, whose charge occupation is “frozen in,” depending on synthesis history. Photostimulation provides the mechanism by which these states equilibrate with the band edges.