The roles of electrons and holes in photo-excited samarium doped titanium dioxide (TiO2:Sm) thin film were investigated with electric measurement techniques. For this purpose, a structural modification using interface states in silicon oxide between TiO2:Sm and a conductive silicon substrate was used. Since the interface states make a barrier to electrons in positive DC bias VDC, selective injection of holes into TiO2:Sm can be realized in VDC>0. Photo-excited dielectric relaxation (PEDR) technique, namely frequency dispersion measurement of complex impedance under excitation light, and the selective injection revealed that the Sm excitation was induced by an electron trapping with a slow response of ∼12 Hz and following recombination with holes in host TiO2 with ∼950 Hz.
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