| Résumé | We present here a theory of excitonic complexes in gated WSe₂ quantum dots (QDs). The QD gate potential causes type-II band alignment, i.e., electrostatically confines holes and repels electrons, or vice versa. Hence, the confinement of excitons involves a delicate balance of the repulsion of electrons by the gate potential with the attraction by the Coulomb potential of the hole localized in the QD. We present a theory of neutral excitonic complexes within a gated WSe₂ QD, considering spin, valley, electronic orbitals, and many-body interactions. We analyze how the electron-hole attraction depends on a range of parameters, such as screened Coulomb interaction, strength of confinement of holes, and repulsion of electrons. Using an atomistic tight-binding model, we compute valence and conduction band states within a computational box comprising over 1 million atoms with applied gate potential. The gate potential is split into a fictitious type-I potential which attracts both the electron and hole and a correction repelling the electron only. The atomistic wave functions are then used to calculate direct and exchange Coulomb matrix elements for a fictitious type-I QD and to obtain a spectrum of interacting electron-hole pairs. Next, the effect of repulsive potential, pulling away the electron from the valence hole, is included in the excitonic basis. This allows us to determine whether electron-hole pairs are sufficiently attracted to overcome electron repulsion by the confinement potential. Finally, we compute the dipole transition between hole and electron states to obtain the absorption spectrum. |
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