Location: Home >> News >> Research Progress  
  Research Progress  
    Insight into Strain Effects on Band Alignment Shifts, Carrier Localization and Recombination Kinetics in CdTe/CdS Core/Shell Quantum Dots
http://www.gaomingyuan.com  Wednesday, Feb 11, 2015  10:00
     Construction of semiconductor/semiconductor core/shell structures has been demonstrated to be one of the most effective ways to improve the photoluminescence (PL) efficiency and tune the PL emission of QDs as well. Nevertheless, the formation of such core/shell structure often leads to strain due to the lattice mismatch between core and shell. At the present, quantitative influences of strain on the electronic structure of QDs remain to be unfold, which is not only fundamentally but also practically interesting.
      The CdTe/CdS core/shell QDs represent a typical strained system due to the substantial lattice mismatch between CdTe and CdS. Herein, we report our recent investigations on theoretical modeling of CdTe/CdS core/shell QDs by a strain-modified effective mass approximation (EMA). In detail, through considering band deformation potential, the core/shell band alignments caused by strain were rectified and then included EMA simulations on electronic level, carrier spatial distribution, and electron-hole wave function overlap. The theoretical results were then carefully compared with experimentally derived data. The most important findings based on the agreement between theoretical and experimental results can be summarized below: 1) the compressive strain on core and tensile strain on shell largely alter the conduction band offset rather than valance band offset of CdTe/CdS QDs, 2) strain largely varies the localization of electron wave function of CdTe/CdS QDs with thick CdS shell (~ 3 monolayers). As a result, the PL emission peak is shifted over a large wavelength range. But fast growth of CdS shell will substantially decrease the PL QY due to the strong extension of electron wave function into the shell in consequence of strain, allowing the underlying non-radiative recombination to compete with the slowed radiative recombination.
      In conclusion, the strain-improved EMA model yields conclusive and constructive insights into band alignment shifts caused by strain, the consequent effects on carrier localization and recombination kinetics of core/shell nanocrystals, and the resulting impact on PL QY. Therefore, the current study could in large perspective be extended to unfold the intricate optical nature of lattice mismatched core/shell QDs and even doped QDs, for rational design of advanced light-emitting nanomaterials.
                                                                                                                                                                                                          Lihong Jing et al.