Structure and thermal stability of InAs/GaAs quantum dots grown by atomic layer epitaxy and molecular beam epitaxy

The structure and thermal stability of self-assembled InAs/GaAs quantum dots (QDs) grown by atomic layer epitaxy (ALE) and molecular beam epitaxy (MBE) QDs were studied using high-resolution electron microscopy with in situ heating experiment capabilities. The ALE QDs were larger and more regular shaped than MBE QDs because of the higher diffusivity of In compared with that of InAs in MBE growth. The QDs were found to form a lens-shaped structure with side facets in the early stage of growth. Upon capping with a GaAs layer, however, the QD apexes flattened because of the diffusion of In and As from the QDs. The structural behavior of QDs at elevated temperatures was observed directly on the atomic scale by in situ heating experiments within TEM. The in situ high-resolution electron microscopy revealed that the uncapped ALE and MBE QDs remained stable up to 580 °C. However, above 600 °C, the QDs collapsed due to the diffusion and evaporation of In and As from the QDs.