Infrared spectroscopy of intraband transitions in self-organized InAs/GaAs quantum dots

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Abstract
We have investigated the midinfrared absorption between confined levels of undoped InAs/GaAs quantum dots obtained by self-organized growth. The infrared absorption is measured by a photoinduced infrared spectroscopy.Quantum dots with different sizes are analyzed as a function of temperature, interband pump photon energy, intensity, and infrared polarization. We show that in the 90–250 meV energy range the quantum dots exhibit intraband absorption between confined levels, which are polarized along the growth axis as for usual conduction intersubband transitions in quantum wells. Intraband absorption is observed for either selective excitation of the dots or excitation via absorption in the wetting and GaAs layers. Based on the energy position and the temperature dependence, the infrared resonances are attributed to intraband transitions between confined holes and to bound-to-continuum transitions of electrons, which, respectively, shift to high and low energy as the dot size is decreased. The reported features are found in qualitative agreement with the theoretical predictions of Grundmann et al. [Phys. Rev. B 52, 11 969 (1995)].