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We have investigated the carrier relaxation in closely vertically stacked InAs quantum dots by time-resolved photoluminescence (PL) and micro-PL measurements. The PL decay and the excitation spectrum in the closely stacked dots are much different with those in single layer dots. The PL decay in the stacked dots strongly depends on the PL energy. The decay time in the lower energy side of the PL increases with the number of stacked dot layers. These suggest the existence of a cascadelike relaxation channel via nonresonant tunneling between the stacked dots. The nonresonant tunneling is consistent with the results of micro-PL measurement which allows us to access single columns of the stacked dots. A broad near-resonant absorption in a single column of the dots is explained on the basis of the nonresonant tunneling. © 2004 American Institute of Physics.