Theoretical Study on the Shape and the Electronic Structure of InP QDs
Kim Dümbgen a, Ivan Infante b, Zeger Hens a
a Physics and Chemistry of Nanostructures group, Department of Chemistry, Ghent University, Belgium
b Istituto Italiano di Tecnologia (IIT), Genova, Italy, Via Morego, 30, Genova, Italy
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#NCFun19. Fundamental Processes in Semiconductor Nanocrystals
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Ivan Infante and Jonathan Owen
Poster, Kim Dümbgen, 436
Publication date: 18th July 2019

Over the last 20 years, indium phosphide quantum dots (InP QDs) have been investigated intensively, thanks to their exceptional photophysical and electronic properties. Nevertheless, the understanding and the control of the properties of these non-toxic nanocrystals is still limited. Notably, only few theoretical studies of InP nanostructures have been reported, and even less simulations of real-sized InP QDs. However, a detailed theoretical analysis can be very beneficial when it comes to explaining the structure, the surface chemistry and the trap state formation of QDs. In this context, we report our results on the theoretical construction, and of density functional theory (DFT) calculations of differently shaped InP nanocrystals of realistic size. In a first study, we investigate how the shape and size of III-V nanocrystals influences the different surface sites and the total charge of the system. We find evidence that large III-V QDs are likely to be in tetrahedral rather than spherical shape. This is due to the surface sites available for negatively charged ligands, which are needed to charge-balance the crystal. This result is in accordance with the existing literature, where tetrahedral InP and InAs nanocrystals of edge lengths up to 10 nm have been reported. Our own experimental work shows that upon the addition of zinc chloride to the synthesis, the QDs tend to stay smaller and exhibit more spherical shapes. An effect which can also be explained by our theoretical models. We further investigate the electronic structure of differently shaped InP QDs upon Z-type ligand displacement by DFT calculations. Our study points out the importance of the geometry of the nanocrystals on the shape of the HOMO and LUMO, which in turn effects the trap state formation. Interestingly, localization of the electronic density occurs both on under-coordinated In and P atoms, which is in contrast to the results obtained for more established II-VI materials.  Our study thus demonstrates the potential of DFT calculations on the understanding of the electronic structure of InP QDs, and it gives an interesting insight into the shape-control of these promising nanomaterials.   

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