Theoretical comparison of the energies and wave functions of the electron and hole states between CdSe- and InP-based core/shell/shell quantum dots: effect of the bandgap energy of the core material on the emission spectrum

Abstract

We theoretically compare the energies and wave functions of the electron/hole states between InP- and CdSe-based core/shell/shell colloidal quantum dots (QDs) and investigate how the bandgap energy of the core material affects the light emission characteristics such as the photoluminescence quantum yield and linewidth. The band diagrams and electron/hole energies of InP/ZnSe/ZnS and CdSe/ZnSe/ZnS QDs, having the same emission wavelength, are calculated on the basis of strain-modified effective mass approximation (EMA). The QD strain distribution, caused by the lattice mismatch, is considered based on the continuum elasticity theory. The energies and wave functions of all the electron and hole states in the InP- and CdSe-based core/shell/shell QDs are obtained through the analytical solution of the Schrodinger equation under the EMA. Then, the emission spectra of the two QDs are calculated while considering the homogeneous and inhomogeneous broadening. Finally, we elucidate why the emission characteristics of InP-based QDs, such as the quantum efficiency and emission linewidth, are inferior to those of CdSe-based QDs, and how these can be improved by using the III-V ternary core materials with a bandgap energy comparable to or larger than that of CdSe.