title: Anomalous independence of multiple exciton generation on different group IV-VI quantum dot architectures.
abstract: Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell. Remarkably, the measured quantum yield of MEG, the hot exciton cooling rate, and the Auger recombination rate of biexcitons are similar for pure PbSe QDs and core/shell QDs with the same core size and varying shell thickness. The higher density of states in the alloy and core/shell QDs provide a faster exciton cooling channel that likely competes with the fast MEG process due to a higher biexciton density of states. Calculations reveal only a minor asymmetric delocalization of holes and electrons over the entire core/shell volume, which may partially explain why the Auger recombination rate does not depend on the presence of a shell.
authors.affiliation: Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands.
authors.forename: M Tuan
authors.initials: MT
authors.lastname: Trinh
authors.forename: Leo
authors.initials: L
authors.lastname: Polak
authors.forename: Juleon M
authors.initials: JM
authors.lastname: Schins
authors.forename: Arjan J
authors.initials: AJ
authors.lastname: Houtepen
authors.forename: Roman
authors.initials: R
authors.lastname: Vaxenburg
authors.forename: Georgy I
authors.initials: GI
authors.lastname: Maikov
authors.forename: Gal
authors.initials: G
authors.lastname: Grinbom
authors.forename: Aaron G
authors.initials: AG
authors.lastname: Midgett
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Luther
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Beard
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Nozik
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.forename: Efrat
authors.initials: E
authors.lastname: Lifshitz
authors.forename: Laurens D A
authors.initials: LD
authors.lastname: Siebbeles
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007854:Lead / Q000737:chemistry*; D008027:Light; D045663:Quantum Dots; D012542:Scattering, Radiation; D018036:Selenium Compounds / Q000737:chemistry*
chemical_list: D018036:Selenium Compounds; C088065:lead selenide; D007854:Lead