Biexciton formation in ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ quantum-dot and quantum-well structures

The dimensionality dependence of the biexciton formation process is investigated by comparing (Cd,Zn)Se/ ZnSe quantum-dot and quantum-well structures using time-resolved photoluminescence (PL) spectroscopy. Modeling the onset of the biexciton PL signal with a system of rate equations, we obtain a biexciton formation coefficient of about $4\times {10}^{-10}{\mathrm{cm}}^2/\mathrm{p}\mathrm{s}$ for 35-nm quantum dots and of $0.2\times {10}^{-10}{\mathrm{cm}}^2/\mathrm{p}\mathrm{s}$ for the quantum-well reference, respectively, indicating a distinct enhancement of the biexciton formation efficiency in quantum dots. By analyzing the spectral line shape of the PL signal, an increase of the biexciton binding energy from 6.4 meV in the case of the quantum-well reference, to 11.3 meV for the quantum dots, is determined.