Band alignment and excitonic localization of ZnO/Cd0.08Zn0.92O quantum wells

Abstract

The band structure and excitonic recombination of a Cd0.08Zn0.92O/ZnO single quantum well (SQW) were shown to vary according to well width (LW). The excitonic localization of a Cd0.08Zn0.92O single layer used as a well layer of the SQW was based on alloy disorder by spatial inhomogeneity of the Cd atoms. It was shown that photoexcited excitons localized into potential fluctuations of 18 meV from a measurement of temperature-dependent photoluminescence (PL), which became an important guide to estimate the degree of excitonic localization for the SQW. The LW of SQW remarkably influenced excitonic localization, which gradually increased with a narrowing of LW. When LW was less than the excitonic Bohr diameter (Rex: 3.6 nm) of ZnO, the excitonic localization was determined by both alloy disorder and interface fluctuations of the barrier/well interfaces. On the other hand, the excitonic localization became remarkably weak for LW greater than Rex mainly because of the quantum-confined Stark effect (QCSE). The formation of the QCSE was clarified by an excitation-power-dependent PL of SQW and an identification of band alignment of a Cd0.08Zn0.92O/ZnO heterostructure. Finally, the excitonic localization of SQW for LW comparable to Rex was determined by the alloy disorder generated in the well.