Neutral donors confined in semiconductor coupled quantum dot-rings: Position-dependent properties and optical transparency phenomenon

Abstract

Electronic properties of a neutral donor confined in a $\mathrm{GaAs}$ coupled quantum dot-ring covered by a ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ matrix were calculated using the finite element method under the effective mass and the envelope function approximations. The proposed model is set up to fit a realistic coupled quantum dot-ring geometry revealed by atomic force microscopy images. The results show that the energy levels and the transition energies in the presence of an electric field strongly depend on the donor center’s angular position. Furthermore, the total optical absorption coefficient is calculated within the two-level approximation and the matrix density formalism. The absorption spectrum shows that the system can be tuned between 5 and $30\mathrm{meV}$. Also, an optical transparency effect for different configurations characterized by specific donor center’s angular positions and electric field values is seen. Finally, a novel redshift is observed when the sample temperature increases.