Evidence of interdot electronic tunneling in vertically coupled In0.4Ga0.6As self-organized quantum dots

Ultrafast differential transmission spectroscopy with a resonant pump revea ls evidence of electronic tunneling among the excited levels of vertically aligned In0.4Ga0.6As self-organized quantum dots. This evidence of tunnelin g is observed as a rapid spectral redistribution of electrons within a few hundred femtoseconds of optical excitation. Measurements show that this spe ctral spread is independent of carrier density and, therefore, indicate tha t carrier-carrier scattering is not the main mechanism for carrier redistri bution. Instead, electronic tunneling is responsible for the interdot coupl ing; tunneling rate calculations agree reasonably with the experiment, supp orting this conclusion. (C) 2000 American Institute of Physics. [S0003-6951 (00)04417-X].