title: Insight into strain effects on band alignment shifts, carrier localization and recombination kinetics in CdTe/CdS core/shell quantum dots.
abstract: The impact of strain on the optical properties of semiconductor quantum dots (QDs) is fundamentally important while still awaiting detailed investigation. CdTe/CdS core/shell QDs represent a typical strained system due to the substantial lattice mismatch between CdTe and CdS. To probe the strain-related effects, aqueous CdTe/CdS QDs were synthesized by coating different sized CdTe QD cores with CdS shells upon the thermal decomposition of glutathione as a sulfur source under reflux. The shell growth was carefully monitored by both steady-state absorption and fluorescence spectroscopy and transient fluorescence spectroscopy. In combination with structural analysis, the band alignments as a consequence of the strain were modified based on band deformation potential theory. By further taking account of these strain-induced band shifts, the effective mass approximation (EMA) model was modified to simulate the electronic structure, carrier spatial localization, and electron-hole wave function overlap for comparing with experimentally derived results. In particular, the electron/hole eigen energies were predicted for a range of structures with different CdTe core sizes and different CdS shell thicknesses. The overlap of electron and hole wave functions was further simulated to reveal the impact of strain on the electron-hole recombination kinetics as the electron wave function progressively shifts into the CdS shell region while the hole wave function remains heavily localized in CdTe core upon the shell growth. The excellent agreement between the strain-modified EMA model with the experimental data suggests that strain exhibits remarkable effects on the optical properties of mismatched core/shell QDs by altering the electronic structure of the system.
authors.affiliation: Institute of Chemistry, Chinese Academy of Sciences , Bei Yi Jie 2, Zhong Guan Cun, Beijing 100190, China.
authors.forename: Lihong
authors.initials: L
authors.lastname: Jing
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Kershaw
authors.forename: Tobias
authors.initials: T
authors.lastname: Kipp
authors.forename: Sergii
authors.initials: S
authors.lastname: Kalytchuk
authors.forename: Ke
authors.initials: K
authors.lastname: Ding
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Zeng
authors.forename: Mingxia
authors.initials: M
authors.lastname: Jiao
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Sun
authors.forename: Alf
authors.initials: A
authors.lastname: Mews
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Rogach
authors.forename: Mingyuan
authors.initials: M
authors.lastname: Gao
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D004583:Electrons; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D055620:Optical Phenomena; D045663:Quantum Dots / Q000737:chemistry*; D011789:Quantum Theory; D013440:Sulfides / Q000737:chemistry*; D013691:Tellurium / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D013440:Sulfides; C034939:cadmium sulfide; D013691:Tellurium; C028337:cadmium telluride