Thermal effect on bound exciton in CdTe/Cd1−xZnxTe cylindrical quantum dots

The temperature dependence of the exciton ground state, lowest and binding energies in cylindrical quantum dot (QD) are theoretically investigated using a variational procedure within the effective mass approximation. The interaction between the charge carriers (electron and hole) and longitudinal optical (LO) phonon modes is taken into account. The excitonic confinement is described by a finite depth potential well. Specific applications of these results are given for CdTe QDs embedded in a CdTe/Cd1-xZnxTeCdTe/Cd1-xZnxTe matrix. The total and lowest energies depend strongly on the temperature, up to a critical value of temperature T (around 40 °K), increasing with it. In the small dot sizes region, both energies decrease rapidly with increasing dot radius and approach the quantum well limit energies for large radius. In addition, an enhancement of the Zn fraction in the barrier material increases both the total and binding energies of the exciton. It is found that the exciton binding energy is significantly reduced with increasing temperature and its effect is more important on the ground state energy than on the binding energy. Moreover the exciton is stable even at room temperature. The LO-phonon contribution to the exciton binding energy is important and depends on the dot size, the Zn fraction and the temperature.