Shallow Donor Impurity States with Excitonic Contribution in GaAs/AlGaAs and CdTe/CdSe Truncated Conical Quantum Dots under Applied Magnetic Field.

Lorenz Pulgar-Velásquez,Ricardo L Restrepo,Juan A Vinasco,Esin Kasapoglu,Alvaro L Morales,John A Gil-Corrales,Adrian Radu,David Laroze,Carlos A Duque,José Sierra-Ortega

doi:10.3390/nano11112832

Lorenz Pulgar-Velásquez, Ricardo L Restrepo + Show 8 more

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https://doi.org/10.3390/nano11112832

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Using the effective mass approximation in a parabolic two-band model, we studied the effects of the geometrical parameters, on the electron and hole states, in two truncated conical quantum dots: (i) GaAs-(Ga,Al)As in the presence of a shallow donor impurity and under an applied magnetic field and (ii) CdSe–CdTe core–shell type-II quantum dot. For the first system, the impurity position and the applied magnetic field direction were chosen to preserve the system’s azimuthal symmetry. The finite element method obtains the solution of the Schrödinger equations for electron or hole with or without impurity with an adaptive discretization of a triangular mesh. The interaction of the electron and hole states is calculated in a first-order perturbative approximation. This study shows that the magnetic field and donor impurities are relevant factors in the optoelectronic properties of conical quantum dots. Additionally, for the CdSe–CdTe quantum dot, where, again, the axial symmetry is preserved, a switch between direct and indirect exciton is possible to be controlled through geometry.

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Low dimensional systems have been some of the most widely investigated objects in semiconductor physics because of their interesting properties and applications, their quantum confinement effects, which have led to different ‘recipes’ for designing novel semiconductor materials for optoelectronic devices [1,2,3,4]
We have studied the electron and hole states in GaAs-(Ga,Al)As conicalshaped quantum dots (QDs) in the presence of an axially located shallow donor impurity under the effects of an externally applied magnetic field and CdSe–CdTe core–shell QDs without impurity and magnetic field effects
The impurity position and the magnetic field direction preserve the axial symmetry of the system

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Introduction

Low dimensional systems have been some of the most widely investigated objects in semiconductor physics because of their interesting properties and applications, their quantum confinement effects, which have led to different ‘recipes’ for designing novel semiconductor materials for optoelectronic devices [1,2,3,4]. The optical and electronic properties of tapered QDs, including the effects of electric and magnetic fields and donor impurities, have been studied in different works [31,32]. Type-II QDs come from a combination of two semiconductors, where the alignment of the energy gaps gives rise to the confinement of electrons and holes in different regions of space. We are interested in studying the electron, shallow donor impurity, and heavy hole exciton states for two kinds of conical QDs: (i) shallow donor impurity states in truncated conical shaped GaAs-(Ga,Al)As QDs, which can be modeled through a Coulomb interaction, in the simple model of a hydrogenic atom, and considering the effects of an externally applied magnetic field. The paper is organized as follows: Section 2 contains the theoretical framework; Section 3 is devoted to the results and corresponding discussion; in Section 4, we present the main conclusions

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