Design of low-lattice-mismatch type-I heterostructures of zinc chalcogenide and synthesis of ZnTeS quantum dots as key materials for realizing green and red emission

Abstract

ZnTeSe alloy based nano-heterostructures exhibit green and red emission and are Cd/Pb-free II–VI quantum dot (QD) phosphors in blue-by-color displays; however, the heterostructures are quasi-type-II confinement heterostructures with underlying large lattice mismatches, resulting in a broad emission band. Although ZnTeS QDs that have homogeneous compositions inside the QD, are essential for realizing type-I-confinement heterostructures, they have not been obtained thus far because of significant differences in the reactivity of the Te and S precursors. In this study, the composition dependence of the energy at the bottom of the conduction band and top of the valence band of ZnTeS alloy semiconductors, that exhibit large band gap bowing, was calculated, and heterostructures that achieve type-I confinement were explored. We designed green- and red-emissive type-I heterostructures with a small lattice mismatch at the interfaces based on this composition dependence and the lattice parameters of the ZnTeS alloy. We succeeded in synthesizing compositionally homogeneous ZnTeS alloy QDs using diethylzinc, bis(trimethylsilyl)telluride, and bis(trimethylsilyl)sulfide as precursors. Large band gap bowing, which agrees with the theoretical prediction, was observed in ZnTeS alloy QDs. This is the first step toward the development of Cd/Pb-free II–VI QD phosphors for blue-by-color displays.