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

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 Mnassisted epitaxial growth. We find an unusually large variation of exciton-biexciton energy difference (3 meV ≤ ∆EX−XX ≤ 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 δ1 and Landé factor. Above results indicate that values of the δ1 and of the Landé 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.

Advanced material system for the design of an intermediate band solar cell: Type-II CdTe quantum dots in a ZnCdSe matrix

“…Using Vegard's law and the known band alignments for these two materials 21,22 , the band structure for the QD region is approximated in figure 5(a). There is a large valence band offset of 0.86 eV between ZnCdSe and CdTe and the large quantum confinement of the holes due to their very small size gives rise to the observed 200 meV energy difference.…”