Controlling Charge Carrier Overlap in Type-II ZnSe/ZnS/CdS Core-Barrier-Shell Quantum Dots.
We describe the synthesis and spectroscopic characterization of colloidal ZnSe/ZnS/CdS nanocrystals, which exhibit a type-II electronic structure and wave function overlap that is strongly dependent on the thickness of the ZnS barrier. Barrier thickness is controlled by both the amount of deposited material and the reaction and annealing temperature of CdS shell growth. The results show that a single monolayer of ZnS mitigates the overlap significantly, while four and more monolayers effectively suppress band edge absorption and emission. Transient absorption spectra reveal a broad distribution of excitons with mixed S and P symmetry, which become allowed due to alloy formation and contribute to charge carrier relaxation across the barrier. We present a model of the core/shell interface based on cation diffusion, which allows one to estimate the extent of the diffusion layer from optical spectra.
†Physical Chemistry, TU Dresden, Bergstraße 66b, 01062 Dresden, Germany.
Klaus
K
Boldt
‡Department of Physics and Astronomy, VU University, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.
Charusheela
C
Ramanan
‡Department of Physics and Astronomy, VU University, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.
Alina
A
Chanaewa
†Physical Chemistry, TU Dresden, Bergstraße 66b, 01062 Dresden, Germany.
Matthias
M
Werheid
†Physical Chemistry, TU Dresden, Bergstraße 66b, 01062 Dresden, Germany.
Alexander
A
Eychmüller
cation exchange; mixed states; overlap integral; potential barrier; transient absorption spectroscopy