Near-infrared emission from spatially indirect excitons in type II ZnTe/CdSe/(Zn,Mg)Te core/double-shell nanowires

Abstract

ZnTe/CdSe/(Zn, Mg)Te core/double-shell nanowires are grown by molecular beam epitaxy by employing the vapor–liquid–solid growth mechanism assisted with gold catalysts. A photoluminescence study of these structures reveals the presence of an optical emission in the near infrared. We assign this emission to the spatially indirect exciton recombination at the ZnTe/CdSe type II interface. This conclusion is confirmed by the observation of a significant blue-shift of the emission energy with an increasing excitation fluence induced by the electron–hole separation at the interface. Cathodoluminescence measurements reveal that the optical emission in the near infrared originates from nanowires and not from two-dimensional residual deposits between them. Moreover, it is demonstrated that the emission energy in the near infrared depends on the average CdSe shell thickness and the average Mg concentration within the (Zn, Mg)Te shell. The main mechanism responsible for these changes is associated with the strain induced by the (Zn, Mg)Te shell in the entire core/shell nanowire heterostructure.

Excitonic fine structure of epitaxial Cd(Se,Te) on ZnTe type-II quantum dots

“…CdSe/ZnTe is a semiconductor system, which is wellknown for its type-II band alignment, in which the spa-tially indirect optical emission appears in the near infrared spectral region, i.e., at 1.0 eV-1.1 eV. This fact has been demonstrated experimentally in CdSe/ZnTe quantum wells [44] and CdSe/ZnTe core/shell nanowires [45]. However, the lattice mismatch which is the driving force for the formation of self assembled QDs is very small and amounts to 0.003 in this material system, which prevents the formation of type II CdSe/ZnTe QDs.…”