Self-assembled semiconductor nanostructures: climbing up the ladder of order

Abstract

Different growth techniques and growth strategies are presented to climb up the hierarchy of order in the field of self-assembled semiconductor nanostructures. In a first step we report a significant improvement of the nanostructure size homogeneity by using either a repetitive desorption and regrowth procedure or by applying extremely low growth rates at high growth temperatures. With this approach an InAs/GaAs quantum dot (QD) ensemble with a height distribution of ±5% and a final photoluminescence (PL) peak line width of 19 meV at room temperature was fabricated. After capping the low growth rate QDs with GaAs, well-developed rhombus-shaped structures with holes in their center are observed. The PL of closely stacked InAs QDs exhibits a line width of 16 meV at low temperature. Remarkable lateral alignment into square arrays of self-assembled SiGe islands with a pronounced size and shape homogeneity is achieved by deposition near their thermodynamic equilibrium using liquid phase epitaxy. The combination of self-assembly with conventional pre-patterning leads to long-range lateral order of In(Ga)As QDs on GaAs(0 0 1). A three-dimensional crystal is fabricated by stacking multiple layers and vertically aligned In(Ga)As QDs onto a pre-patterned GaAs(0 0 1) substrate. The structure shows good PL properties at room temperature.