Regensburg 2010 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 47: New Materials: mainly thermoelectric and nanomechanical Properties

HL 47.5: Vortrag

Mittwoch, 24. März 2010, 17:00–17:15, H14

Crossover between Type II and Type I Alignment in Layered Hybrid Assemblies of CdSe and CdTe Nanocrystals — •Andreas Pöschl¹, Dieter Gross¹, Christian Mauser¹, Andrei Susha², Andrey Rogach², Enrico Da Como¹, and Jochen Feldmann¹ — ¹Photonics and Optoelectronics Group, Physics Department and CeNS, Ludwig-Maximilians-Universität, München, Germany — ²Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong

Semiconductor nanocrystals (NCs) feature variable band gaps controlled by the quantum confinement. Reducing the size of the NCs increases the band gap. This effect is used to tune layered assemblies of CdSe and CdTe NCs between charge separation and energy transfer processes. Considering the bulk energy levels, CdSe and CdTe exhibit a type II interfaces alignment. Previously, we have shown that assemblies of large CdSe NCs and CdTe NCs provide charge separation processes, investigated by photoluminescence (PL) quenching. In this work the size of the CdSe NCs is varied. Increasing the band gap of the CdSe NCs from 2.4 to 2.7 eV yields a transition from type II to type I interface with CdTe NCs of 2.1 eV band gap. Because of the unfavorable alignment for charge transfer, energy transfer processes from the CdSe to the CdTe NCs are observed by PL spectroscopy. The use of smaller CdTe NCs with 2.2 eV band gap restores the type II alignment. These optical investigations demonstrate a facile method to probe the crossover form type II to type I in NCs assemblies and therefore the relative band alignment.