Absence of the bowing character in the common-anion II-VI ternary alloys

The absence of bandgap bowing in the common-anion II-VI semiconductor ternary alloys is investigated. As examples, we consider the Cd1-xZnxTe and Cd1-xZnxSe alloys. The sp3s* tight-binding method with the inclusion of spin-orbit interactions is employed to calculate the alloy's band structure and its corresponding constituents' charge states (ionicities) as a function of composition. The variation is found to be nearly linear. The vanishingly small valence-band offset (VBO≅0) in common-anion compounds would yield a linear scaling of bandgap energy with composition, especially as the conduction-band edge state being a singlet state with spherical symmetry. Furthermore, the two cation atoms (Cd and Zn) are found not to compete in changing their charge states as the composition is varied. The absence of such competition is believed to be the main reason for the absence of bowing. The theoretical results are compared to the available experimental data and found to be in good agreement.