Study of the Formation Mechanism of Self-Assembled Quantum Dot Arrays with a Focus on Alloying and Nucleation Control

摘要

The objective of the research project is to further the understanding of key materials science with regard to the formation mechanism of semiconductor self assembled quantum dots via epitaxy. During the funding period of 3+ years, we have made significant progress in that direction. We have conducted in-depth study on the following specific topics: the importance of alloying during epitaxial growth of SAQDs; the function of buried misfit dislocation in guided self-assembly by epitaxy; key issues pertinent to the growth of III-V on Si(001); and finally, the feasibility of fabricating quantum dot lasers of InAs or GaAs on Si. The importance of alloying was studied using the combination of Ge SAQD on Si in which the critical dot size for pyramid-to- dome transition was shown to increase significantly with increasing intermixing between Ge and Si. Using a buried misfit dislocation network, we have been able to demonstrate three distinctively different types of nucleation sites on Si(001). Furthermore, a properly designed, partially relaxed SiGe buffer layer has been shown to be a valuable vehicle for studying the formation mechanism of Ge SAQDs on Si. One of the applications was to experimentally determine the diffusion constant of Ge on Si and on Sb covered Si. We have also shown that the growth of III-V on Si is via Vomer-Weber mode without a wetting layer. Furthermore, the critical dot size for dislocation of InAs SAQDs on Si is less than 5 nm, making it a fundamental hurdle for fabricating lasers on Si.