Investigation of Many-Body Correlation in Biexcitonic Systems Using Electron-Hole Multicomponent Coupled-Cluster Theory

Generation of biexcitons in semiconductor nanoparticles has important technological applications in designing efficient light-harvesting materials. Like excitons, the attractive electron-hole interaction terms are responsible for binding in biexcitonic systems. However, unlike excitons, electron-electron and hole-hole repulsive components also contribute to the overall interaction in a biexcitonic system. Consequently, a balanced treatment of many-body correlation associated with electron-electron, hole-hole, and electron-hole interactions is needed for understanding quaisparticle binding in biexcitons. This work presents a theoretical investigation of the effect of size and chemical composition on biexciton binding energies in semiconductor nanoparticles using the electron-hole multicomponent coupled-cluster theory (eh-mcCC). Exciton and biexciton binding energies for quantum dots with diameters 1-20 nm for four semiconductor materials (CdSe, CdS, CdTe, and PbS) were calculated using the eh-mcCC method. The calculated exciton and biexciton binding energies were found to be in good agreement with previously reported experimental results for quantum dots. The results from these calculations demonstrate that exciton and biexciton binding energies exhibit very different scaling behavior with respect to increasing dot diameter. Specifically, with increasing dot diameter, exciton binding energies were found to decrease following a power-law dependence. By contrast, the biexciton binding energies were found to decrease exponentially and decreased at a slower rate as compared to exciton binding energies. The dramatic difference between the scaling equations for the exciton and biexciton binding energies shows that the response of the biexcitonic system with respect to change in the confinement potential is fundamentally very different from the response shown by excitonic systems.