Compositional and size-dependent spectroscopic shifts in charged self-assembled ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots

Atomistic pseudopotential many-body calculations of excitonic (X) recombination in charged, self-assembled ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ dots predict and explain remarkable trends. (i) The redshift of the exciton energy upon negative charging is rapidly reduced with increasing the In content and increasing the dot height. The opposite behavior is observed upon positive charging. (ii) The recombination peak energies of different charge states show intriguing symmetries and alignments, e.g., $X^{-}$ aligns with $X^{2-}$ and $X^{3-}$ aligns with $X^{4-}.$ (iii) The $X^{3-}$ spectrum shows that a triplet initial state is lower in energy for flat dots (yielding two spectral lines), whereas the singlet state is lower in energy for taller dots (yielding a single line). These trends are explained theoretically in terms of a crossover occurring at a critical In concentration and dot height at which the electron wave functions becomes more localized than the hole wave functions.