Power dependent photoluminescence of lateral quantum dot molecules: Indication of extended electron states

Excitation power density dependent photoluminescence (PL) measurements of an ensemble of ordered lateralquantum dot (QD) molecules containing on average 4 and 8 QDs are carried out. Asymmetric broadeningof the PL spectra is observed with increasing excitation power density which is stronger for 8 QDsper molecule than for 4 QDs. In addition, a shift of the PL peak to higher energies occurs. In p-type modulation-doped QD molecules the asymmetric broadening and high-energy shift are enhanced. N-type modulation-doped QD molecules exhibit a square-shaped PL spectrum, resembling that of modulation-dopedquantum wells. These findings are consistently explained by state filling in the presence of extended electronstates due to lateral electronic coupling of the QDs within the molecules forming a quasi twodimensionaldensity of states.