Thickness-Dependent Charge Carrier Dynamics in CdSe/ZnSe/CdS Core/Barrier/Shell Nanoheterostructures.
We report the synthesis of CdSe/ZnSe/CdS heterostructures composed of type I and type II band alignments, where ZnSe acts as a barrier for charge carriers between the CdSe core and the CdS shell as well as being an active component of the type I (CdSe/ZnSe) and type II (ZnSe/CdS) structure simultaneously. We investigated the effect of the thickness of the barrier and the shell on the charge carrier dynamics by using UV/Vis absorbance, photoluminescence (PL), and time-resolved fluorescence techniques. The experimental data are supported by simple theoretical calculations based on effective mass approximation (EMA). PL results indicate the emission from both type I and type II structures. Time-resolved fluorescence studies show that the lifetime of the core emission decreases with increasing barrier width, owing to a greater confinement of the exciton to the core, whereas it increases with shell width because of the tunneling of charge carriers, primarily electrons, delaying the recombination of the exciton. The lifetime of the shell emission decreases with shell width as well as barrier width and height, with a larger effect being observed for the barrier width and negligible for the associated changes in the barrier height.
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
Sushma
S
Yadav
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
Apurba
A
Chowdhury
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India. sapra@chemistry.iitd.ac.in.
Sameer
S
Sapra
charge dynamics; heterostructures; photoluminescence; quantum dots; semiconductors