Hole trap state analysis in SrTiO3

Abstract

We have analyzed the temperature and time dependences of the photoconductivity response of SrTiO₃ single crystals and thin films. We observe a sharp increase in photoconductivity at 35 K and infrared quenching of the photocurrent below this temperature. We use a simple two-level sensitization model to show that the low-temperature photocurrent is controlled by hole trapping at shallow sensitizing centers within 100 meV of the valence band top. We assign these defect sites to intrinsic Sr vacancies in SrTiO₃. This work shows that photoconductivity measurement is an effective tool for determining the location and density of acceptor-type defects close to the top of the valence band. This technique is useful for analyzing the effectiveness of p-type doping in wide band gap oxide semiconductors for developing hydrogen evolution photocatalysts that have visible light response.