Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper‐Bound to 99.85% by Ion–Solid Interactions

Abstract

to new applications arising from the control of single charges and spins on individual dopants in silicon. Promi sing applications are where the donors function as quantum bits (qubits). How ever, configuring materials with arrays of single donor qubits in the solid state is a formidable challenge. It has been proposed that noisy, intermediatescale quantum (NISQ) [1] devices with ≈50-100 qubits can surpass classical supercom puters in executing some specific algo rithms. [2] Even for NISQ devices, the error budgets for the physical qubits are strict, requiring errors well below 1% in order to achieve sufficient circuit depths. Beyond NISQ, errorcorrected, universal quantum processors of the kind necessary to run Shor's factoring algorithm on a 2000 bit classical key will require upwards of 4000 logical qubits. Using a 2D surface code architecture, this would translate to about 200 mil lion physical qubits with present error rates of around 0.1%. [3] Future devices with lower error rates [4] will reduce the required number of physical qubits. The surface code is also able to tolerate 5-10% physically nonfunctional (absent or faulty) qubits in the architecture. [5,6] Silicon chips containing arrays of single dopant atoms can be the material of choice for classical and quantum devices that exploit single donor spins. For example, group-V donors implanted in isotopically purified 28 Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31 P, hyperfine clock transitions in 209 Bi or electrically controllable 123 Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here, an on-chip detector electrode system with 70 eV root-mean-square noise (≈20 electrons) is employed to demonstrate near-room-temperature implantation of single 14 keV 31 P + ions. The physics model for the ion-solid interaction shows an unprecedented upper-bound single-ion-detection confidence of 99.85 ± 0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31 P + implants, a yield limit of 98.1% is demonstrated. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single-ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202103235.

Fabrication of $^{15}\textrm{NV}^{-}$ centers in diamond using a deterministic single ion implanter

“…The latter results in a low energy dispersion, important for avoiding chromatic aberration when focusing by electric field lenses. Additionally, our method uses singly charged ions at energies lower than 10 keV, unlike methods that rely on the detection of single ion impact events [15]. The low energy implantation reduces position uncertainty due to straggling and surface destruction of the bulk diamond.…”

“…Along the axial direction, the trap is encapsulated by two pierced end-caps with a length of 10 mm, allowing for the extraction of the ions by switching them to high voltage. The ion gun serves as a source for molecular 15 N + 2 ions, which are loaded into the linear Paul trap together with atomic Ca + ions from an oven. A Wien filter after the ion gun (not shown) may be used.…”

“…In case of a higher charge to mass ratio compared to calcium, the dark ion e.g. 15 N 2 will arrive earlier at the endcap. At the moment the dark ion is inside the endcap, the voltage of the endcap is switched to a positive value, deflecting the calcium ion back when approaching the endcap.…”

“…For an unambiguous determination of the dark ion species, i.e. to identify the trapped particle as a successfully loaded 15 N + 2 molecular ion, we extract theions and detect them after a flight of 428 mm in length using a secondary electron multiplier with an efficiency of 96±2 %. During ion extraction, we switch off the RF amplitude, to avoid shot-to-shot modifications of the ion trajectory.…”

“…Since each single nitrogen ion is trapped and identified prior to implantation, After carefully purging all tube connections between 15 N 2 gas bottle and ion gun we found no indication for 14 N + 2 ions. However, after a waiting time of 5 days, the histogram shows a peak at mass 28, which was assigned to the isotope 14 N. b) Velocity variations of 40 Ca (purple) and 15 N 2 (blue) ions as a function of delay between RF and DC switching. Ions with a mass of 40 and 30, respectively, arrive at different times at the position of the endcap hole, and explore different phases of the RF drive field.…”