Proceedings of nanoGe September Meeting 2017 (NFM17)
Publication date: 20th June 2016
Semiconductor nanoplatelets are the colloidal analogue of epitaxial quantum wells. Despite several similarities, the opto-electronic properties of nanoplatelets present remarkable differences with respect to those of quantum wells. In this work, we provide theoretical assessment on the main physical factors inducing such differences: (1) the presence of lateral confinement, (2) the presence of an organic environment dielectrically mismatched with the inorganic structure and (3) the possibility of growing heterostructures not only along the direction of strong confinement, but also along the weakly confined directions.
By means of a simple semi-analytical, effective mass method, we calculate exciton emission and binding energies, wave function and radiative lifetime for core-only, core-shell and core-crown nanoplatelets with CdSe core. In general, the physics is severely dependent on the strength of electron-hole correlation, which in these systems is enhanced by dielectric confinement.
We show that nanoplatelets with lateral dimensions under 20 nm fall in an intermediate confinement regime, where the emission energy can be blueshifted by tens of meV -in agreement with experiments[1]-, and radiative lifetimes are shorter than quantum well expectations. For typical experimental sizes, we estimate radiative lifetimes of 1 ps or less are feasible, thus supporting related four-wave-mixing experiments.[2]
In core-shell CdSe/CdS nanoplatelets, charge separacion is efficient, but in core-crown ones the strong Coulomb interaction keeps both carriers confined by the core, and the exciton physics resembles that of core-only nanoplatelets, which explains the spectral response resported in Ref.[3].
References
[1] Bertrand et al. Chem. Commun. 52, 11975 (2016).
[2] Naeem et al. Phys. Rev. B 91, 121302(R) (2015).
[3] Tessier et al. Nano Lett. 14, 207 (2014).
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