Towards Quantum Dot Crystals via Multilayer Stacking on Different Indexed Surfaces

Abstract

The growth of InGaAs on GaAs with sufficient lattice mismatch typically proceeds in the Stranski–Krastanov (SK) mode. In the SK growth mode, the first few monolayers (MLs) of InGaAs form a pseudomorphic twodimensional (2D) layer, traditionally called the wetting layer (WL). After a critical thickness, the development of three-dimensional (3D) InGaAs islands, which partially relieve the built-up strain, is more energetically favorable than continuous layers. Such 3D islands standing on the 2D WL, usually referred to as self-assembled quantum dots (QDs), have been commonly used for low-dimensional semiconductor research in the last decade. Generally, the InGaAs QDs are randomly distributed on the 2D WL due to the stochastic nature of the self-assembly process. The resulting selfassembled InGaAs QDs have emerged as an important class of materials with potential for modern optoelectronic devices, such as QD-based lasers and detectors. In principle, however, more control over uniformity and spatial organization of the InGaAs QD arrays is desirable for many applications. For example, organized 3D arrays are important for addressing QDs and for a collective behavior uniquely different from the individual InGaAs QDs.

For the vertical ordering along the growth direction, the SK growth mode has produced excellent results through stacking of multiple InGaAs layers and the corresponding strain interaction through GaAs spacer layers.