Critical barrier thickness for the formation of InGaAs/GaAs quantum dots

Abstract

The discovery of self-assembled quantum dots (QDs) has attracte because of its possible applications in optoelectronic devices. The low density of QDs formed makes it useful to grow several layers of dots in the form of a stacked structure. In these structures, the buried islands tend to influence the further nucleation of islands in subsequent layers. It has been experimentally found that, when the number of layers increases, island sizes and shapes become more regular with each successive layer. Theoretical models have been proposed to elucidate the correlated vertical self-organization. The Stranski–Krastanow (SK) growth produces a tensile region, which induces the preferential nucleation of the next SK island just above the buried 3D-island. Experimental evidence of strain below the quantum dots (QDs) has induced us to study the influence of very thin barrier GaAs layers on InGaAs/GaAs QDs structures. This In diffusion due to strain defines the Critical Barrier Thickness for the formation of quantum wells from three dimensional islands. A Critical Barrier Thickness of 6 nm was observed in the case of 1.8 nm In0.5Ga0.5As/GaAs QDs structures. Above this thickness stacked QDs show near perfect alignment, whilst below this thickness modulated QWs are observed. The structural behaviour is supported by photoluminescence (PL) characteristics.