Submonolayer Quantum Dots

The cycled deposition of small InAs islands into a GaAs matrix leads to the formation of a tailored rough quantum well containing densely spaced In-rich agglomerations referred to as submonolayer quantum dots, which support an efficient exciton formation. Carrier localization properties of the submonolayer structures are further enhanced by alloying with antimony. In this chapter we address the growth, the structure, and the optical and optoelectronic properties of alloyed and unalloyed InAs submonolayer quantum dots and devices based on these structures. Based on structural and optical characterization, we find densities of localization centers exceeding those of self-assembled quantum dots by an order of magnitude. Submonolayer quantum dots show quantum-dot like ultrafast carrier dynamics, while at the same time providing a significantly larger modal gain, which reaches values known for InGaAs quantum-well structures. We develop a numerical model for the density of states and relevant scattering channels in the submonolayer potential landscape. Alloyed and unalloyed submonolayer quantum dots differ predominantly in the degree of hole localization, which is dramatically increased by the addition of antimony. We show that the alloyed submonolayer quantum dots support a heterodimensional confinement, from fully zero-dimensional to hetero-confinement with zero-dimensionally confined holes and electrons free in two dimensions.