Versatile direct-writing of dopants in a solid state host through recoil implantation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-10-07 |
| Journal | Nature Communications |
| Authors | Johannes E. Fröch, Alan Bahm, Mehran Kianinia, Zhao Mu, Vijay Bhatia |
| Institutions | Thermo Fisher Scientific (United States), The University of Sydney |
| Citations | 23 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research introduces Recoil Implantation via Focused Ion Beam (FIB) as a versatile, mask-free technique for ultra-shallow, site-selective doping in solid-state hosts.
- Core Method: Momentum transfer from an inert, accelerated primary ion beam (Xe+ FIB) to atoms within a pre-deposited thin film (dopant precursor), resulting in the implantation of the secondary species into the underlying target.
- Ultra-Shallow Profiles: The technique yields dopant profiles localized to the top few nanometers of the target surface, with maximum photoluminescence (PL) observed at a mean depth of less than 1.5 nm.
- High Positional Accuracy: Demonstrated lateral placement accuracy for dopant ensembles is (44 ± 4) nm, which is sufficient for integration into high-field regions of advanced photonic devices.
- Elemental Versatility: Successful creation of optically active color centers using a wide range of elements, including the Group IV family (SiV, GeV, SnV, PbV) in bulk diamond.
- Geometric Flexibility: The method is applicable to non-planar substrates, proven by the direct implantation of Europium (Eu3+) rare earth ions into the core of a commercial single-mode optical fiber.
- Engineering Relevance: This mask-free, direct-write capability is ideal for engineering near-surface states, shallow doping of single electron transistors, and modifying atomically-thin materials.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Primary Ion Beam | Xe+ (Plasma FIB) | N/A | Momentum transfer source |
| Ion Acceleration Voltage | 30 | keV | Standard operating condition |
| Ion Beam Current | 10 | pA | Standard operating condition |
| Precursor Film Thickness | 15 | nm | Used for Group IV dopants on diamond |
| Positional Accuracy (Mode) | 44 ± 4 | nm | Lateral placement precision (GeV ensemble) |
| Dopant Depth (PL Max) | <1.5 | nm | Measured mean depth of maximum GeV luminescence |
| Dopant Depth (Tail Limit) | 8 ± 2 | nm | Measured depth limit of residual PL signal |
| Annealing Temperature | 950 | °C | Post-implantation activation |
| Annealing Pressure | <2 x 10-6 | Torr | High vacuum condition |
| SiV Zero Phonon Line (ZPL) | 738 | nm | Optically active defect emission in diamond |
| GeV Zero Phonon Line (ZPL) | 602 | nm | Optically active defect emission in diamond |
| Eu3+ Emission Wavelength | 620 | nm | 5D0 â 7F2 transition in optical fiber |
| SiV Excited State Lifetime | 1.5 ± 0.1 | ns | Photophysical property |
| GeV Excited State Lifetime | 4.7 ± 0.1 | ns | Photophysical property |
Key Methodologies
Section titled âKey MethodologiesâThe recoil implantation process utilizes a dual FIB-SEM system and involves the following key steps:
- Substrate Cleaning: Electronic grade diamond (<1 ppb Nitrogen) is cleaned using hot (150 °C) Piranha Acid (H2SO4:H2O2 2:1) for at least 2 hours.
- Dopant Precursor Deposition: Thin films (typically 15 nm thick) of the desired dopant material (e.g., Si, Ge, Sn, Pb, Eu) are deposited onto the target surface using magnetron sputtering or thermal evaporation.
- Recoil Implantation (Direct Writing): A 30 keV Xe+ focused ion beam (FIB) operating at 10 pA is electrostatically scanned across the precursor film. Momentum transfer implants the dopant atoms into the underlying host material (e.g., diamond).
- Fluence Example: Xe+ fluence for SiV activation was typically 5 x 1013 cm-2.
- Thin Film Stripping: The residual precursor film is chemically removed using sequential cycles of strong acids and bases (KOH, HCl, and Piranha Acid) to eliminate surface residue.
- Defect Activation (Annealing): The sample is annealed in a tube furnace under high vacuum (pressure less than 2 x 10-6 Torr) at 950 °C for 2 hours to promote the formation of fluorescent defect complexes (color centers).
- Depth Verification (EBIE): Electron Beam Induced Etching (EBIE) using H2O vapor in an environmental SEM is employed to gradually etch a wedge into the implanted area, allowing correlation of depth (measured by AFM) with photoluminescence intensity (PL).
Commercial Applications
Section titled âCommercial ApplicationsâThe versatility and precision of recoil implantation make it highly relevant across several advanced technology sectors:
- Quantum Information and Sensing:
- Deterministic creation of Group IV color centers (SiV, GeV, SnV, PbV) in diamond, which serve as optically addressable qubits for quantum computing and robust sensors.
- Engineering of near-surface states in semiconductor devices for quantum applications.
- Integrated Photonics:
- Site-specific integration of quantum emitters into photonic structures (e.g., 2D photonic crystal cavities) due to sub-50 nm positional accuracy.
- Doping optical fiber cores with rare earth elements (like Eu3+) for integrated quantum memories and active fiber components.
- Nanoelectronics:
- Ultra-shallow doping required for fabricating single electron transistors (SETs) and other nanoscale electronic devices where surface proximity is critical.
- Advanced Materials Engineering:
- Electronic and magnetic doping of atomically-thin materials (e.g., graphene, transition metal dichalcogenides) where conventional implantation methods are ineffective or cause excessive damage.
- Spintronics:
- Controlled introduction of magnetic elements for engineering magnetism at the nanoscale.
View Original Abstract
Abstract Modifying material properties at the nanoscale is crucially important for devices in nano-electronics, nanophotonics and quantum information. Optically active defects in wide band gap materials, for instance, are critical constituents for the realisation of quantum technologies. Here, we demonstrate the use of recoil implantation, a method exploiting momentum transfer from accelerated ions, for versatile and mask-free material doping. As a proof of concept, we direct-write arrays of optically active defects into diamond via momentum transfer from a Xe + focused ion beam (FIB) to thin films of the group IV dopants pre-deposited onto a diamond surface. We further demonstrate the flexibility of the technique, by implanting rare earth ions into the core of a single mode fibre. We conclusively show that the presented technique yields ultra-shallow dopant profiles localised to the top few nanometres of the target surface, and use it to achieve sub-50 nm positional accuracy. The method is applicable to non-planar substrates with complex geometries, and it is suitable for applications such as electronic and magnetic doping of atomically-thin materials and engineering of near-surface states of semiconductor devices.