Effect of shell thickness on exciton and biexciton binding energies in ZnSe/ZnS core/shell quantum dot

The exciton and biexciton binding energies are calculated for a ZnSe/ZnS core/shell quantum dot incorporating WKB approximation. With the variations in shell thickness, the exciton binding energy shows nonlinear behavior. A maximum value of exciton binding energy is expected to occur for shell thickness equals to the core radius. Similar results are reported for biexcitons where for thicker shells the biexciton attains antibonding. Corresponding to an increase in binding energy, a red shift in the PL spectra is expected which is compatible with the experimental observations.