Paul Räcke | Searcharxiv

arXiv2023

Graphene-Enhanced Single Ion Detectors for Deterministic Near-Surface Dopant Implantation in Diamond

Colour centre ensembles in diamond have been the subject of intensive investigation for many applications including single photon sources for quantum communication, quantum computation with optical inputs and outputs, and magnetic field sensing down to the nanoscale. Some of these applications are realised with a single centre or randomly distributed ensembles in chips, but the most demanding application for a large-scale quantum computer will require ordered arrays. By configuring an electronic-grade diamond substrate with a biased surface graphene electrode connected to charge-sensitive electronics, it is possible to demonstrate deterministic single ion implantation for ions stopping between 30 and 130~nm deep from a typical stochastic ion source. An implantation event is signalled by a charge pulse induced by the drift of electron-hole pairs from the ion implantation. The ion implantation site is localised with an AFM nanostencil or a focused ion beam. This allows the construction of ordered arrays of single atoms with associated colour centres that paves the way for the fabrication of deterministic colour center networks in a monolithic device.

cond-mat.mes-hall↗

arXiv2022

Near-Surface Electrical Characterisation of Silicon Electronic Devices Using Focused keV Ions

The demonstration of universal quantum logic operations near the fault-tolerance threshold establishes ion-implanted near-surface donor atoms as a plausible platform for scalable quantum computing in silicon. The next technological step forward requires a deterministic fabrication method to create large-scale arrays of donors, featuring few hundred nanometre inter-donor spacing. Here, we explore the feasibility of this approach by implanting low-energy ions into silicon devices featuring an enlarged 60x60 $μ$m sensitive area and an ultra-thin 3.2 nm gate oxide - capable of hosting large-scale donor arrays. By combining a focused ion beam system incorporating an electron-beam-ion-source with in-vacuum ultra-low noise ion detection electronics, we first demonstrate a versatile method to spatially map the device response characteristics to shallowly implanted 12 keV $^1$H$_2^+$ ions. Despite the weak internal electric field, near-unity charge collection efficiency is obtained from the entire sensitive area. This can be explained by the critical role that the high-quality thermal gate oxide plays in the ion detection response, allowing an initial rapid diffusion of ion induced charge away from the implant site. Next, we adapt our approach to perform deterministic implantation of a few thousand 24 keV $^{40}$Ar$^{2+}$ ions into a predefined micro-volume, without any additional collimation. Despite the reduced ionisation from the heavier ion species, a fluence-independent detection confidence of $\geq$99.99% was obtained. Our system thus represents not only a new method for mapping the near-surface electrical landscape of electronic devices, but also an attractive framework towards mask-free prototyping of large-scale donor arrays in silicon.

cond-mat.mes-hall↗