Electron-detrapping from localized states in the band gap of (Ba,Sr)TiO3

We tried to relate the relaxation currents of Pt/62 nm-thick-(Ba0.5Sr0.5)TiO3/Pt capacitors to the results of ultraviolet photoemission spectroscopic measurements for the 62 nm-thick-(Ba0.5Sr0.5)TiO3/Pt specimens. The slowest relaxation (159–313 s at applied voltages of 1.5–3 V, and at a measuring temperature of 40 °C) and the relatively faster relaxations (4.92–5.43 and 0.25–0.46 s) were assigned as the electron-detrapping from the localized state at 0.80 eV below the quasi-Fermi level, from the localized state at 0.55 eV below the quasi-Fermi level, and from the localized state at 0.30 eV below the quasi-Fermi level, respectively. The decrease in the relaxation time caused by the increase in bias voltage is probably due to the decreasing depletion width. The decrease in depletion width is probably due to the detrapping of electrons from deep localized states in accordance with the downward bending of quasi-Fermi level in the depletion layer. The bending is produced by the decrease in relative dielectric constant in the depletion layer in accordance with the increasing of bias voltage.