Electric-field control of exciton fine structure in alloyed nanowire quantum dot molecules

Abstract

Alloyed ${\mathrm{InAs}}_{0.2}{\mathrm{P}}_{0.8}/\mathrm{InP}$ nanowire quantum dot molecules reveal nontrivial electric-field evolution of the bright-exciton spectra; this was studied here using the atomistic theory. For a quantum dot molecule composed of two nanowire quantum dots of dissimilar sizes, the overall field dependence resembles the typical self-assembled quantum dot molecule spectra with an avoided crossing of direct and indirect excitons. However, for coupled nanowire quantum dots of identical dimensions and chemical compositions---where the bright-exciton splitting is triggered by alloy randomness---the notion of direct/indirect excitons is mostly lost, with the bright-exciton splitting field evolution varying strongly between various random realizations of nominally identical systems. Nonetheless, for several random samples, lower-higher excitonic branch mixing leads to the reduction of bright-exciton splitting below the $1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{eV}$ threshold but with the restoration of pronounced optical activity away from the crossing. Thus, a simultaneous reduction of the bright-exciton splitting, without the detrimental reduction in the lower excitonic branch optical activity, makes alloyed nanowire quantum dot molecules a possible platform for applications in quantum optics and information.