Exciton spectra in vertical stacks of triple and quadruple quantum dots in an electric field

We study an electron-hole pair in a stack of multiple quantum dots in the presence of an external electric field using the configuration-interaction approach. We find that the bright energy levels can be grouped into families which are associated with the hole localized in a specific dot of the stack. The exciton energy levels undergo avoided crossings as function of the external electric field with different patterns for each family. We show that the variation of the depths of the dots along the stack can be deduced from the exciton spectrum. For stronger coupling the families are mixed by a weak electric field due to hole tunneling. This results in a characteristic multiple avoided crossing of energy levels belonging to different families with an accompanying modulation of the recombination probabilities and an appearance of a single particularly bright state. Discussion of a simple modeling of these avoided crossings is provided.