The impact of stochastic incorporation on atomic-precision Si:P arrays

Abstract

Scanning tunneling microscope lithography can be used to create nanoelectronic devices in which dopant atoms are precisely positioned in a Si lattice within ∼1 nm of a target position. This exquisite precision is promising for realizing various quantum technologies. However, a potentially impactful form of disorder is due to incorporation kinetics, in which the number of P atoms that incorporate into a single lithographic window is manifestly uncertain. We present experimental results indicating that the likelihood of incorporating into an ideally written three-dimer singledonor window is 63 ± 10% for room-temperature dosing, and corroborate these results with a model for the incorporation kinetics. Nevertheless, further analysis of this model suggests conditions that might raise the incorporation rate to near-deterministic levels. We simulate bias spectroscopy on a chain of comparable dimensions to the array in our yield study, indicating that such an experiment may help confirm the inferred incorporation rate.

Hole in one: Pathways to deterministic single-acceptor incorporation in Si(100)-2$\times$1

“…Given the computationally prohibitive difficulty of modeling the full dissociation to incorporation pathway, for all simulations we count a bridging BH, BCl, or AlCl on the silicon surface as an eventual incorporation, and all other fragments as non-incorporation events. This mirrors a similar treatment for phosphine from Warschkow et al [77], for which Ivie, Campbell, Koepke et al recently demonstrated agreement with incorporation rates inferred from STM scans for phosphine single donor incorporation within three dimer wide windows [63] that were consistent with prior analyses [78]. In all cases, the adsorption energies of these bridging fragments are so low (typically below -2.0 eV) and the re- on the same dimer row(s), however, we assume that these dopants will dimerize and become electrically inactive and do not count these as incorporations within our model.…”

“…In other words, the process of a single acceptor incorporating with atomic-precision must be deterministic, not stochastic, to be realistically scalable. Previous work on phosphine has estimated this singledonor incorporation percentage at ≈ 65% when dosed at room temperature, although corroborating kinetic modeling revealed a potential pathway toward deterministic incorporation by increasing the dosing temperature to ∼ 150 °C [63].…”

Room temperature donor incorporation for quantum devices: arsine on germanium

“…In all previously studied systems an incorporation anneal (typically 350 • C) is required in order for the donor atoms to adopt substitutional lattice sites in the surface 13,20,38 . However, this anneal is highly undesirable as it provides a route for the desorption of the donors from the surface, and presents a major obstacle to the scale up to large-scale quantum technological devices 21,22 . Arsine on germanium solves this problem, since the donor atoms are completely substitutionally incorporated into the surface spontaneously upon adsorption at room temperature, and no incorporation anneal is required.…”

“…The probability of successfully incorporating phosphorus into silicon using a hydrogen resist was studied by two independent groups and determined to be P incorp. ∼ 70% 21,22 . Since the probability for successfully fabricating N qubits scales as (P incorp. )…”