Monolithic Growth of Ultrathin Ge Nanowires on Si(001)

Abstract

Self-assembled Ge wires with a height of only 3 unit cells and a length of up to 2 micrometers were grown on Si(001) by means of a catalyst-free method based on molecular beam epitaxy. The wires grow horizontally along either the [100] or the [010] direction. On atomically flat surfaces, they exhibit a highly uniform, triangular cross section. A simple thermodynamic model accounts for the existence of a preferential base width for longitudinal expansion, in quantitative agreement with the experimental findings. Despite the absence of intentional doping, the first transistor-type devices made from single wires show low-resistive electrical contacts and single-hole transport at sub-Kelvin temperatures. In view of their exceptionally small and self-defined cross section, these Ge wires hold promise for the realization of hole systems with exotic properties and provide a new development route for silicon-based nanoelectronics.

Influence of composition and substrate miscut on the evolution of {105}-terminated in-plane Si1−xGex quantum wires on Si(001)

“…Also, the base width b = 15 ± 2 nm is in excellent agreement with the values reported in Ref. 24. The base width is at no stage significantly affected by the wire composition.…”

“…Wire bundles consisting of just two QWs could be demonstrated in this way. 22 Similar bundles 23 24 SiGe hut clusters were among the first SK islands studied in the Si/Ge heterosystem. 25,28 In contrast to pyramid-shaped islands, they have a rectangular base area and a ridge oriented along one of the two equivalent 100 directions in the (001) substrate plane ( Fig.…”

“…The isolated QWs developing from hut clusters during annealing preserve both the average base width and its narrow variance, even though their length can have extended by two orders of magnitude. 24 In a recent attempt to model this observation, Montalenti et al compared the energetics of different wire geometries. 34 They took into account the volumetric strain energy, ab initio surface energies of the strained {105} facets, and estimated edge energies taken from their earlier work on 551 oriented wire bundles on Si(1 1 10).…”

Continuum modelling of semiconductor heteroepitaxy: an applied perspective

“…A close inspection of the island shape reveals fascinating oscillations [23]. Interestingly, shape oscillations were also obtained in the absence of dislocations, as due to intermixing [24]. Actually, despite being favoured by entropy, intermixing is yet another channel leading to strain relaxation as alloying lowers the effective lattice mismatch between film and substrate [25,26].…”

“…The most striking example is given by Ge{105} whose surface energy is stabilized by compression [43][44][45] to the point that the (001) wetting layer can spontaneously break into {105} faceting [7,46]. Micron-long, horizontal Ge wires delimited by {105} facets, have been recently observed [24,47] and shown to display peculiar electronic properties.…”