Strain Engineering in InP/(Zn,Cd)Se Core/Shell Quantum Dots

The formation of core/shell structures has become an established approach to passivate the surface and enhance the photoluminescence quantum yield of semiconductor nanocrystals, quantum dots. However, lattice mismatch between the core and the shell materials results in surface reconstructions at the core/shell interface and compressive or tensile strain in the core and the shell. Concomitantly formed surface traps can have a negative impact on the emission properties. Growing buffer layers with intermediate lattice constants or using alloys to tune the lattice constant is often considered to reduce the reconstruction-induced strain. We present a study that quantitatively relates strain and shell composition in the case of InP/(Zn,Cd)Se core/shell quantum dots. We apply Raman spectroscopy to quantize strain and find that adjusting the composition of the (Zn,Cd)Se shell tunes the strain from compressive to tensile. The transition between both regimes is found at shell compositions where the bulk lattice constants of InP and (Zn,Cd)Se match, which confirms that matching lattice constants is a viable strategy to achieve strain-free core/shell nanocrystals.