Self-assembled InAs quantum dots on cross-hatch InGaAs templates: Excess growth, growth rate, capping and preferential alignment

Abstract

Self-assembled InAs quantum dots (QDs) are grown on cross-hatch GaAs/InGaAs templates via molecular beam epitaxy with systematic variations in the degree of excess growth, growth rate and capping of the QD layer. Standard epitaxy (SE) with excess growth and migration-enhanced epitaxy (MEE) at high growth rates result in the formation of uniform, high-density InAs QDs on the InGaAs cross-hatch layer. When overgrown or capped by a thin GaAs layer, these QDs undergo shape transformation where quantum dashes and wires along the [1 1 0]- and [1 −1 0] directions are simultaneously formed as a result of chemical potential gradient and anisotropic strain fields. When the underlying InGaAs cross-hatch layer is covered by a thick GaAs spacer layer, subsequent growth of InAs QDs via SE or MEE results in preferential alignment of QDs along the [1 1 0]- or [1 −1 0] direction, respectively. This is attributed to the asymmetries in the underlying cross-hatch and adatoms mobility. The various size, density, shape and alignment distributions of QDs on cross-hatches provide means for engineering of optoelectronic devices.