Excitonic lifetimes in (Zn,Cd)Se/ZnSe and ZnSe/Zn(Se,S) quantum wires

Recombination dynamics in dry-etched (Cd,Zn)Se/ZnSe nanostructures: Influence of exciton localization

“…In deep etched wires and dots, the reduction of the exciton lifetime and the normalized PL intensity with decreasing size is usually explained by a diffusion of free excitons to the sidewalls followed by a nonradiative recombination process at the surface. [9][10][11][13][14][15][16][17][18] This picture is confirmed by experimental data, e.g., for GaAs/͑Al,Ga͒As wires 14,16 and dots, 18 ZnSe/Zn͑Se,S͒ wires, 17 and CdTe/͑Cd,Zn͒Te wires. 10 However, there are recent reports on ͑Cd,Zn͒Se/ZnSe wire structures, 17,19 where the recombination lifetime observed in time-resolved PL spectroscopy remains approximately constant even if the lateral size is reduced down to 20 nm.…”

“…Obviously, this simple diffusion model is not appropriate to explain the sizedependent biexponential decay observed in our samples. In addition, the diffusion model is also unable to explain the experimental findings in wet etched Cd 0.35 Zn 0.65 Se/ZnSe wires, 17 where no significant reduction of the lifetime was obtained even for 20 nm wide wires.…”

“…Usually the lateral size dependence of the recombination dynamics in various deep etched III-V 14,16,18 and II-VI 10,17 nanostructures, respectively, is explained taking into account exciton diffusion to the sidewalls and subsequent nonradiative surface recombination. Using such a model a predominantly monoexponential decay characteristics with a size dependent time constant is obtained.…”

“…Thus, the size-dependent exciton lifetimes in wires and dots are mainly controlled by the diffusion constant D and the surface recombination velocity S. Experimentally, this situation is realized, e.g., for GaAs/͑Al,Ga͒As wires or ZnSe/Zn͑S,Se͒ wires as reported in the literature. 16,17 In contrast, if the density of localized states N L exceeds the number of excitons per unit area significantly ͑corre-sponding to vϭ100) an almost monoexponential decay within a time constant given by the radiative lifetime of localized excitons is obtained. In this case, the decay time is found to be independent of the wire width.…”

“…Experimentally, such a behavior was observed in wet etched Cd 0.35 Zn 0.65 Se/ZnSe wire structure, as reported recently. 17,19 At this point, it is instructive to discuss the size dependence of the normalized PL intensity for this situation, which can be evaluated easily from our calculations. Although no reduction of the exciton recombination time is obtained for decreasing wire width, carrier loss at the wire sidewalls can occur during the relaxation process of excitons into localized states, reducing the PL intensity in narrow wires.…”