Hybrid functionals study of band bowing, band edges and electronic structures of Cd_{1- x}Zn_xS solid solution

We have systematically studied band bowing, band edges, and electronic properties of both zinc-blende and wurtzite Cd_1-xZn_xS solid solutions by using a special quasirandom structures approach combined with hybrid DFT calculations. Hybrid DFT gives a more accurate description of the lattice constants, formation enthalpies, and electronic structures of the parent semiconductors than standard DFT. Alloying CdS with ZnS causes a downward band bowing that is dominated by volume deformation. The conduction- and valence- band edges straddle the redox potentials of (O₂/H₂O) and (H⁺/H₂) over the whole Zn concentration range. The high photocatalytic activity of Cd_1-xZn_xS is due to the elevation of the conduction band minimum (CBM). The optimal Zn content is around 0.5, determined as a result of balancing the elevation of the CBM and the widening of the band gap. The valence bandwidth increases with Zn content and thus raises the mobility of photogenerated holes, which may be related to photocorrosion and lead to the leaching of Zn in Cd_1-xZn_xS photocatalyst during water splitting.