Effect of doping electrons on the electronic structure of LaxSr1-xTiO3 studied by ultraviolet photoemission spectroscopy

Effect of doping electrons on the electronic structure of single-crystalline LaxSr1-xTiO3 samples (x=0.001, 0.01, 0.05) has been studied for the fractured surface by ultraviolet photoemission spectroscopy (UPS). Two peaks in the band gap region of SrTiO3 (in-gap peaks) are induced by La substitution for Sr; a peak with a sharp Fermi cut-off(metallic peak) and a broad peak centered at similar to 1.5 eV below E(F) (similar to 1.5 eV peak). The spectral intensity of the metallic peak and the similar to 1.5 eV peak increases with the carrier concentration, but the spectral width of the metallic peak does not depend upon it. The behaviors of doping electrons on the electronic structure near E(F) of LaxSr1-xTiO3, such as no change in the spectral width of the metallic peak and the appearance of the similar to 1.5 eV peak, can not be simply explained by the band theory.