In(Ga)As/GaAs site-controlled quantum dots with tailored morphology and high optical quality

In this article, we describe epitaxial growth and investigations of optical properties of In(Ga)As/GaAs site-controlled quantum dots (QDs) fabricated on (001)-oriented GaAs substrates. The QD nucleation is directed by pre-patterning planar GaAs surfaces with shallow nanoholes. The focus of this work lies on the realization of arrays of site-controlled QDs (SCQDs) with a tailored morphology and optical properties comparable to QDs fabricated on planar substrates. By maximizing the migration length during QD deposition, we were able to increase the QD pitches to values exceeding device dimensions of typical semiconductor microresonators. The introduction of a seeding layer in our growth scheme allows us to extend the vertical distance between the QDs and the etched nucleation centres to about 20 nm without suffering from nanoholes being occupied by multiple QDs. Furthermore, the extended distance between the QD layer and the re-growth interface allows us to preserve excellent optical properties of the single QDs as probed in photoluminescence with an average single QD related linewidth of 133 mu eV and minimum values as low as 25 mu eV for non-resonant excitation. The high yield of optically active QDs on the pre-defined nucleation positions is studied by cathodoluminescence (CL) with high spatial resolution. We find emission from single SCQDs on more than 90% of the nucleation centres, which is a pre-requisite for any scalable QD-device fabrication scheme. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim