Dynamic hole trapping in InAs/AlGaAs/InAs quantum dot molecules

Charges and spins confined in quantum dots and quantum dot molecules are of great interest for new optoelectronic device applications. The strong confinement in quantum dot structures leads to unique interactions among electrons and holes. A detailed understanding of the magnitude and dynamics of these charge-carrier interactions will be essential to the development of future devices. We present experimental evidence of holes trapped in metastable higher-energy states of InAs/AlGaAs/InAs quantum dot molecules. We present a model for the kinetic pathways that lead to this dynamic hole trapping and analyze the consequences of dynamic hole trapping for carrier relaxation and optical emission.

Figure 1

(a) Schematic band diagram of the QDM sample. (b) Detailed schematic of QDM composition and size and lowest confined energy levels for electrons and holes in the two QDs of the QDM.

Figure 2

Energy of emitted PL as a function of electric field. Symbols indicate different charge states: neutral exciton state ($X^0$, black triangles), biexciton ($X{X}^0$, red diamonds), doubly negatively charged trion ($X^{2-}$, blue squares). Open green circles and solid purple circles originate from charge states with a dynamically trapped hole in the bottom QD.

Figure 3

Kinetic pathways that results in optical emission from $X^0$ states with and without dynamically trapped holes.

Figure 4

Left: Lifetime of the electron in the bottom dot as the function of electric field. Right: Ratio of intensity of PL emission from states without and with the presence of a dynamically trapped hole.

Figure 5

The x pattern for the $X^{2-}$ state.

Figure 6

Dynamic pathways to create different spatial configurations of the $X^{2-}$ state with and without the extra dynamic trapped hole.

Figure 7

PL for biexciton states. Blue dashed lines are simulation of the commonly observed biexciton PL from a typical InAs/GaAs QDM.