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.