Regensburg 2019 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 47: Quantum dots and wires: Optical properties II

HL 47.5: Vortrag

Freitag, 5. April 2019, 10:30–10:45, H34

Optical spectroscopy of type-II semiconductor ZnSe/CdS dot-in-rod nanostructures — •Hans Werners, Sven Lohmann, Christian Strelow, Alf Mews, and Tobias Kipp — Institut für Physikalische Chemie, Universität Hamburg, Germany

In type-II semiconductor heterostructures the band offset leads to a spatial separation of electrons and holes. This charge separation makes type-II systems particularly useful, e. g., as light-harvesting materials in photovoltaic devices. Nanoparticles consisting of a spherical ZnSe core surrounded by a rod-shaped CdS shell, so-called dot-in-rods (DRs), represent a quantum system with an intrinsic type-II band alignment at the core/shell interface. This should allow for an efficient manipulation of exciton properties by, e.g., external fields.

We use time-, energy-, and space-resolved confocal fluorescence spectroscopy at room and cryogenic temperatures to investigate individual ZnSe/CdS DRs. The DRs show a high photostability while emitting linearly polarized light at about 2.16 eV, with quantum yields above 35%. Compared to the more conventional type-I CdSe/CdS DR system [1], ZnSe/CdS DRs exhibit increased fluorescence lifetimes. At 8 K, the lifetime is decreased compared to room temperature measurements. Furthermore, at low temperature, we observe abrupt spectral shiftings of the emission line over time, superimposed on smoother spectral diffusion processes. The spectral diffusion covers a larger range in energy than for type-I CdSe/CdS DRs, indicating the larger susceptibility of type-II structures to external stimuli, like surface charges.

[1] S. Lohmann et al., ACS Nano 11, 12185-12192 (2017).