Kinetic Size Selection Mechanisms in Heteroepitaxial Quantum Dot Molecules

Abstract

Heteroepitaxial growth of Si(0.7)Ge(0.3)/Si(001) films under kinetically limited conditions leads to self-assembly of fourfold quantum dot molecules. These structures obtain a narrowly selected maximum size, independent of film thickness or annealing time. Size selection arises from efficient adatom trapping inside the central pit of the quantum dot molecule when the surrounding islands cojoin to form a continuous wall. Self-limiting growth of nanostructures has significant implications for novel nanoelectronic device architectures such as quantum cellular automata.

Beyond the heteroepitaxial quantum dot: Self-assembling complex nanostructures controlled by strain and growth kinetics

“…At this stage the island shape stabilizes and then the QDM size is further maintained by the kinetic effect described earlier and in Ref. 18 The QDM also exhibits an inverse scaling with the mismatch strain ͑or Ge content͒. The challenge is to find the right deposition conditions to produce preferential pit formation as a function of the strain.…”

“…18 As shown in Fig. 6, the QDM lateral ͑and vertical͒ dimensions become fixed at film thicknesses near 20 nm, and the distribution changes very little with additional deposition to over 50 nm thickness, or with annealing at T dep .…”

“…This apparent stability does not arise from any aspect of the energetics; we hypothesized that the formation of the bounding wall prevents escape of adatoms in the pit, thereby preventing further growth of the QDM. 18 However, we have recently analyzed the mass conservation associated with QDMs, and the result suggests that the Fig. 3.…”

Bridging the length scales between lithographic patterning and self assembly mechanisms in fabrication of semiconductor nanostructure arrays

“…u . Equally, as the QDMs evolve to a narrow distribution of shapes and sizes [19], we can accurately control the spacing between QDMs, as illustrated in Figure 5(b).…”

“…Such a basis is the Quantum Dot Molecule (QDM), a complex nanostructure that evolves spontaneously during growth under conditions of limited adatom mobility in the Ge x Si 1-x / Si(100) system [18][19][20][21]. It comprises a four fold set of quantum dots bound elastically to a central pit, Figure 5 (ii) At this point, strain relieving pits start to form, which are shallower than the film thickness and are thus assumed to not be directly associated with contamination at the original growth surface.…”