Lateral carrier transfer in ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{Se}/{\mathrm{ZnS}}_y{\mathrm{Se}}_{1-y}$ quantum dot layers

Lateral carrier transfer is investigated for single ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{Se}/{\mathrm{ZnS}}_y{\mathrm{Se}}_{1-y}$ quantum dots (QD’s) in a high-density ensemble by time-resolved spectroscopy. Following nonresonant excitation a significant probability of independent capture of electrons and holes in separate QD’s is observed. The subsequent lateral migration of carriers between adjacent QD’s leads to a slow decay component of the exciton ground-state luminescence. At low temperatures the lateral carrier transfer is restricted to phonon-assisted inter-QD tunneling, resulting in migration times of the order of several nanoseconds. The role of independent carrier capture is suppressed at high excitation densities or increased temperatures, enabling thermally activated migration.