Conditions for self-assembly of quantum fortresses and analysis of their possible use as quantum cellular automata
Thomas E. Vandervelde, Ryan M. Kalas, P. Kumar, Takeshi Kobayashi, T. L. Pernell, John C. Bean · Journal of Applied Physics · 2005
In this study, we detail the conditions that result in the generation of self-assembled quantum fortresses (QFs), in SiGe∕Si. A QF consists of four quantum dots (QDs) clustered around a central square pit, one QD per side. This structure strongly resembles the proposed quantum cellular automata (QCA) unit cell—the basis for a computer architecture. We map the growth conditions (epilayer thickness and Ge concentration) under which self-assembly of strain-stabilized QFs and their precursors occur. Additionally, we characterize how QFs change in height, width, and internal size scales within this parameter space. From this information, we develop a phenomenological model for why QFs form based upon changes in lattice spacing. We then calculate how QFs of the observed shapes and sizes would function as QCAs based on a Hubbard-type Hamiltonian model. This analysis reveals that self-assembled QFs grown at 550°C, a rate of 1Å∕s, a SiGe alloy composition of 37–40%, and a thickness of 15–35nm could be used as QCAs.