Mechano-electronic Superlattices in Silicon Nanoribbons

Abstract

Significant new mechanical and electronic phenomena can arise in single-crystal semiconductors when their thickness reaches nanometer dimensions, where the two surfaces of the crystal are physically close enough to each other that what happens at one surface influences what happens at the other. We show experimentally that, in silicon nanomembranes, through-membrane elastic interactions cause the double-sided ordering of epitaxially grown nanostressors that locally and periodically highly strains the membrane, leading to a strain lattice. Because strain influences band structure, we create a periodic band gap modulation, up to 20% of the band gap, effectively an electronic superlattice. Our calculations demonstrate that discrete minibands can form in the potential wells of an electronic superlattice generated by Ge nanostressors on a sufficiently thin Si(001) nanomembrane at the temperature of 77 K. We predict that it is possible to observe discrete minibands in Si nanoribbons at room temperature if nanostressors of a different material are grown.

An analytical model for the growth of quantum dots on ultrathin substrates

“…It can be seen that the wavelength becomes increasingly dependent on the substrate thickness as its thickness c decreases below 0 / 2f͑͒. Such a decrease in the QD spacing with decreasing substrate thickness has been observed by Ritz et al 2 for Ge QDs on 6 and 23 nm Si nanomembranes. …”

“…Recently, it has been shown that some control of the QD size and spacing can be achieved through varying the thickness of the substrate. 2,3 The energetics of the system are strongly affected when the thickness of the substrate is comparable with the QD length scale. For ultrathin substrates, such as nanomembranes, 2,4 significant stress relief can arise due to bending of the substrate.…”

“…If QDs are simultaneously deposited on both sides they can interact through the substrate to create a vertically anticorrelated QD structure. 2 In this paper the ATG instability model is extended to consider growth of QDs on ultrathin substrates to quantify how the substrate thickness affects the QD size and spacing and their spatial correlation.…”

Amplitude expansion of the binary phase-field-crystal model

“…After these bottom-side dots are formed they in turn create preferential regions for a new set of dots to nucleate on the top (above their edges) and the process repeats. In such a fashion the process leads to the correlated dot growth as observed in experiments of Ge or SiGe islands on Si membranes [43,44]. This phenomenon can in principle be exploited to create periodic strained nanostructures that in turn produce periodically modulated band gaps.…”

“…This result occurs as the strained quantum dots partially relax by straining the substrate membrane and thinner membranes are easier to deform than thicker ones. Such mechanism has been proved to play an important role in engineering the self assembly of thin film nanostructures such as quantum dots [43].…”