Resonant quenching of photoluminescence in InxGa1-xAs/AlyGa1-yAs/GaAs self assembled quantum dots

We investigated a large series of self-assembled InAs and InxGa1-xAs quantum dot (QD) structures by means of photoluminescence (PL) and PL excitation (PLE) techniques. A pronounced dip of the QD PLE spectra just below the GaAs absorption edge has been observed in all the investigated samples, denoting a resonant quenching of the QD PL intensity. PL spectra with excitation in such spectral region show, beside the QD PL band, a new extrinsic band at 1.356 eV with strong GaAs-LO phonon replicas. The PLE spectrum of this extrinsic band is almost specular to the QD PLE, denoting a competition in the carrier capture between the QDs and the defects associated with the 1.356 eV emission. The chemical etching of the QD and of the surrounding barrier layers does not eliminate the extrinsic PL band, which is, therefore, attributed to a native defect of the GaAs buffer. The spectral position and shape of the 1.356 eV band allows us to associate it to a complex of Ga vacancy with deep acceptor states in the GaAs layers. We conclude that the resonant PL quenching of QDs arises from the competition in the carrier capture between the QDs and deep defects in the GaAs layers. (C) 2002 Elsevier Science B.V. All rights reserved.