Strong valence-band offset bowing of ZnO1-xSx enhances p-type nitrogen doping of ZnO-like alloys

Photoelectron spectroscopy, optical characterization, and density functional calculations of ZnO1-xSx reveal that the valence-band (VB) offset E-v(x) increases strongly for small S content, whereas the conduction-band edge E-c(x) increases only weakly. This is explained as the formation of local ZnS-like bonds in the ZnO host, which mainly affects the VB edge and thereby narrows the energy gap: E-g(x=0.28)approximate to E-g(ZnO)-0.6 eV. The low-energy absorption tail is a direct Gamma(v)->Gamma(c) transition from ZnS-like VB. The VB bowing can be utilized to enhance p-type N-O doping with lower formation energy Delta H-f and shallower acceptor state in the ZnO-like alloys.