All-optical charge initialization concept in a type-II QD array. (a) Schematics of two spatially indirect excitons, XL and XR, sharing a common hole in adjacent QDs formed by a type-II band alignment. Black circles represent electrons and white circles represent holes. (b) Two-stage process of charge initialization in an array of QDs. First, an electron–hole pair is generated in a long-lived configuration in a “Charging region”. Secondly, the charges are transferred along the QD array, electrons to the “Electron region” and holes to the “Hole region”. These two stages are repeated to initialize multiple charges within the structure.