The role of defects in the persistent photoconductivity of BaSnO₃thin films

Time-dependent photoconductivity (PC) and PC spectra have been studied in oxygen deficient BaSnO₃thin films grown on different substrates. X-ray spectroscopy measurements show that the films have epitaxially grown on MgO and SrTiO₃substrates. While on MgO the films are nearly unstrained, on SrTiO₃the resulting film is compressive strained in the plane. Electrical conductivity in dark is increased in one order of magnitude for the films on SrTiO₃in comparison to the one on MgO. This leads to an increase of PC in the latter film in at least one order of magnitude. PC spectra show a direct gap with a value ofEG=3.9eV for the film grown on MgO while on SrTiO₃EG=3.36eV. For both type of films, time-dependent PC curves show a persistent behavior after illumination is removed. These curves have been fitted employing an analytical procedure based on the frame of PC as a transmission phenomenon showing the relevant role of donor and acceptor defects as carrier traps and as a source of carriers. This model also suggests that in the BaSnO₃film on SrTiO₃more defects are created probably due to strain. This latter effect can also explain the different transition values obtained for both type of films.