Strong Valence-Band Offset Bowing of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>ZnO</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:math>Enhances<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-Type Nitrogen Doping of ZnO-like Alloys

Photoelectron spectroscopy, optical characterization, and density functional calculations of ${\mathrm{ZnO}}_{1\ensuremath{-}x}{\mathrm{S}}_{x}$ 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: ${E}_{g}(x=0.28)\ensuremath{\approx}{E}_{g}(\mathrm{ZnO})\ensuremath{-}0.6\text{ }\text{ }\mathrm{eV}$. The low-energy absorption tail is a direct ${\ensuremath{\Gamma}}_{v}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{c}$ transition from ZnS-like VB. The VB bowing can be utilized to enhance $p$-type ${\mathrm{N}}_{\mathrm{O}}$ doping with lower formation energy $\ensuremath{\Delta}{H}_{f}$ and shallower acceptor state in the ZnO-like alloys.

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