Effect of electron-hole separation on optical properties of individual Cd(Se,Te) Quantum Dots

TL;DR

This study investigates how electron-hole separation influences the optical properties of individual Cd(Se,Te) quantum dots, revealing significant variability in excitonic features linked to electron and hole localization.

Contribution

We demonstrate a method to grow low spectral density Cd(Se,Te)/ZnSe quantum dots and analyze how electron-hole spatial separation affects their optical characteristics.

Findings

Large variation in exciton-biexciton energy difference (3-26 meV).

Strong correlation between exciton-biexciton energy difference and exciton recombination rate.

Electron-hole localization impacts fine structure splitting and Landé factor.

Abstract

Cd(Se,Te) Quantum Dots (QD) in ZnSe barrier typically exhibit a very high spectral density, which precludes investigation of single dot photoluminescence. We design, grow and study individual Cd(Se,Te)/ZnSe QDs of low spectral density of emission lines achieved by implementation of a Mn-assisted epitaxial growth. We find an unusually large variation of exciton-biexciton energy difference (3 meV $\leq$ $\Delta \mathrm{E_{X-XX}}$ $\leq$ 26 meV) and of exciton radiative recombination rate in the statistics of QDs. We observe a strong correlation between the exciton-biexciton energy difference, exciton recombination rate, splitting between dark and bright exciton, and additionally the exciton fine structure splitting $\delta_1$ and Land\'e factor. Above results indicate that values of the $\delta_1$ and of the Land\'e factor in the studied QDs are dictated primarily by the electron and hole respective spatial shift and wavefunctions overlap, which vary from dot to dot due to a different degree of localization of electrons and holes in, respectively, CdSe and CdTe rich QD regions.