Competition between initial- and final-state effects in valence- and core-level x-ray photoemission of Sb-doped ${\mathrm{SnO}}_2$

High resolution valence- and core-level photoemission spectra of undoped and 3% Sb-doped ${\mathrm{SnO}}_2$ are presented. Conduction-band occupation due to Sb doping in ${\mathrm{SnO}}_2$ leads to a shift of valence-band features to high binding energy. However, the shift is less than the width of the occupied part of the conduction band. This is attributed to a shrinkage of the bulk band gap with doping, arising from an attractive dopant electron interaction and screening of the Coulomb repulsion between valence and conduction electrons. Core-level spectra provide evidence for strong screening by the conduction electron gas in 3% Sb-doped ${\mathrm{SnO}}_2,$ giving rise to “screened” and “unscreened” final-state peaks in photoemission. The dominant screening response involves excitation of conduction electron plasmons.