Composition dependence of the valence-band states in III-VI and IV-VI solid solutions

We report on a study of the valence-band states in $\mathrm{Ga}{\mathrm{S}}_x{\mathrm{Se}}_{1-x}$ compounds and in $\mathrm{Sn}{\left({\mathrm{S}}_x{\mathrm{Se}}_{1-x}\right)}_2$ compounds by photoemission spectroscopy using linearly-polarized synchrotron radiation. The changes of the valence-states binding energies with $x$ are always smooth but much larger for $\mathrm{Ga}{\mathrm{S}}_x{\mathrm{Se}}_{1-x}$ than for $\mathrm{Sn}{\left({\mathrm{S}}_x{\mathrm{Se}}_{1-x}\right)}_2$. For the $\mathrm{Ga}{\mathrm{S}}_x{\mathrm{Se}}_{1-x}$ family some of these effects are related to the "cationic" or "anionic" character of the corresponding valence-band states while the anomalous behavior observed for the states at the top of the valence band appears related to composition-induced changes in their atomic-orbital character.