Papers by Keyword: Persistent Photoconductivity

Abstract: CuO thin films were obtained through thermal oxidation of dc magnetron sputtered metallic Cu films on glass substrates. Thermal oxidation process was performed in air at temperature ranging 300-500 °C. From XRD patterns, CuO single phase of monoclinic structure was formed at oxidation temperature beyond 450 °C whereas amorphous phase with very small grains was obtained at oxidation temperature below 450 °C. The positive sign of the Hall coefficient confirmed the p-type conductivity in all studied films. From transmission spectra, direct band gap value is varied between 2.17 and 2.83eV. From the transient photoconductivity measurements, persistent photoconductivity (PPC) behavior was observed. The decay current data were better fitted with the multiple exponential functions resulting into five slow decay times. Density of trap states corresponding to its decay time was also evaluated from the decay current data.

Abstract: The decay kinetics of a persistent photoconductivity (PPC) in undoped semi-insulating 4H SiC and intercenter charge transfer were studied with EPR, photo-EPR and optical admittance spectroscopy (OAS). A thermally activated charge transfer process that occurs in the dark has been observed. The PPC effect was observed directly in changes in the quality factor of the EPR cavity before and after illumination and by the decay of the OAS signal for deep levels, and indirectly by the excitation and decay of the nitrogen and boron EPR lines that were not observed in the dark before illumination. The decay kinetics of the PPC and photo-induced carrier capture by nitrogen and boron levels were found to follow a stretched exponential form. The PPC in the temperature range from 77 to 300K was found to be produced by a thermally induced charge transfer process involving deep trap levels.

Abstract: We investigated the influence of photoexcited nonequilibrium electrons in Bi4Ti3O12-d which contains a high density of oxygen vacancies. As increasing oxygen deficiency, the photocurrent undergoes a rapid enhancement, accompanied by a remarkable change of kinetics. In heavily oxygen deficient Bi4Ti3O12-d (d=0.45), we observed dispersive photoconductivity, a behavior resembles with persistent photoconductivity phenomena in some perovskites. We argue that oxygen vacancies acting as trapping centers for electrons are linked to dispersive diffusion in the perovskite blocks, which control carrier recombination.