Exciton-phonon interaction in CdSe and CuCl polar semiconductor nanospheres

We present a theoretical study of the effect of longitudinal-optical phonons and surface-optical phonons on the electronic states of conduction electrons and donorlike excitons in a spherical semiconductor quantum dot. The effect of the quantum confinement is described by an infinitely deep potential well in the framework of the envelope-function approximation associated with two nondegenerate bands. The charge-carrier--phonon coupling is treated within the adiabatic approximation. A variational calculation of the ground-state energy of the donorlike exciton is performed using a one-parameter trial envelope function, which includes electron-hole correlation effects. The results show that in the case of a donorlike exciton located at the center of the microsphere, the effect of the lattice polarization gives rise to a lowering of the absolute value of the energy for all values of the microsphere radius R. The Huang-Rhys factor S, which is a measure of the charge-carrier--phonon interaction and the extent of the charge-carrier density, has been determined as a function of R. For the donorlike exciton, S reaches a minimum value, respectively, equal to S₀=0.2 for R₀=12.7 nm and S₀=3.1 for R₀=2.3 nm in the case of CdSe and CuCl.