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The radiative lifetime dependence on the dot size in multilayer ͑In,Ga͒As quantum dot structures with different thickness GaAs barriers was studied via photoluminescence. In the structure with thick barriers and isolated dots, the radiative lifetime increased monotonically with the dot size, which was attributed to the enhanced exciton oscillator strength in smaller dots. By contrast, in the structure with thin barriers and electronically coupled vertically adjacent dots, the radiative lifetime increased and later decreased with increasing dot size. This can be explained by the enhancement of the exciton oscillator strength in larger dots, which are coherently coupled through vertical tunneling.

This letter reports on theoretical calculations of the oscillator strength associated with electron intraband transitions in (In,Ga)As/GaAs quantum dots. We study the effect of dot size and lateral separation between adjacent dots on the oscillator strength. The calculations indicate that transitions induced by p-polarized light from the electronic ground state to the first excited state are stronger than those induced by s-polarized light for large size dots with wide lateral interdot spacing. This situation changes, however, for small size dots in close proximity with one another. We discuss the relevance and implication of these results for applications in quantum-dot structures designed for mid-infrared detection.