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Abstract: We investigate acceptor and donor states in GaN nanocrystals doped with asingle substitutional impurity. Quantum dots QD-s of zinc-blende structureand spherical shape are considered with the radius ranging from 4.5 to 67.7 A.The size-dependent energy spectra are calculated within the sp3d5s*tight-binding model, which yields a good agreement with the confinement-inducedblue shifts observed in undoped QD-s. The computed binding energy is stronglyenhanced with respect to the experimental bulk value when the dopant is placedat the center of the smallest QD-s. It decreases with increasing QD sizefollowing a scaling law that extrapolates to the bulk limit. In order toestimate the degree of localization of the bound carriers we analyze their wavefunctions and average radii. The resulting physical picture points to a highlylocalized acceptor hole, mostly distributed over the nearest-neighbor anionshell, and a much more extended donor electron. We also study off-centerimpurities in intermediate-size QD-s. The acceptor binding energy isapproximately independent of the dopant position unless it is placed within asurface shell of thickness of the order of the bulk Bohr radius, where theionization energy abruptly drops. On the contrary, the donor binding energygradually decreases as the impurity is moved away from the center toward the QDsurface.



Author: C. Echeverría-Arrondo, J. Pérez-Conde, A. K. Bhattacharjee

Source: https://arxiv.org/







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