Versatile direct-writing of dopants in a solid state host through recoil implantation

At a Glance

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

Technical Documentation & Analysis: Versatile Direct-Writing of Dopants in Diamond

This document analyzes the research paper “Versatile direct-writing of dopants in a solid state host through recoil implantation” (Nature Communications, 2020) to highlight the critical role of high-quality MPCVD diamond and to position 6CCVD as the ideal material supplier and engineering partner for replicating and advancing this quantum technology research.

Executive Summary

Novel Doping Technique: Demonstration of mask-free, site-selective direct-writing of Group IV (Si, Ge, Sn, Pb) and Rare Earth (Eu) dopants into diamond using Focused Ion Beam (FIB) recoil implantation.
Ultra-Shallow Profiles: The technique yields ultra-shallow dopant profiles, with Monte Carlo simulations showing over 90% of implanted species localized within the top 1 nm of the diamond surface, crucial for near-surface quantum sensing applications.
High Positional Accuracy: Achieved high lateral placement accuracy, with the ensemble position distribution yielding a mode of (44 ± 4) nm, which is sufficient for integration into high-field regions of photonic devices.
Material Versatility: Successfully created optically active, single-photon emitting color centers (SiV, GeV, SnV, PbV) in electronic-grade Single Crystal Diamond (SCD).
Methodology: Utilizes momentum transfer from a 30 keV Xe⁺ FIB to pre-deposited 15-nm thin films, followed by high-vacuum annealing at 950 °C for defect activation.
Complex Geometry Capability: Demonstrated applicability to non-planar substrates by implanting Eu³⁺ ions directly into the core of a single-mode optical fiber, a challenge for standard lithography.
6CCVD Value Proposition: Replication and extension of this research requires ultra-high purity, low-strain SCD substrates with superior surface finish (Ra < 1 nm), a core specialty of 6CCVD.

Technical Specifications

Parameter	Value	Unit	Context
Host Material	Electronic Grade SCD	N/A	<1 ppb Nitrogen content
Dopant Precursor Thickness	15	nm	Sputtered thin films (Si, Ge, Sn, Pb)
Primary Ion Beam	Xe⁺	N/A	Focused Ion Beam (FIB)
Acceleration Voltage	30	keV	Xe⁺ beam energy
Beam Current	10	pA	Used for irradiation
Ion Fluence Range (Tested)	5 x 10¹² to 2.5 x 10¹⁵	cm^-2	Range for observable color center formation
Positional Accuracy (Mode)	44 ± 4	nm	Lateral placement precision (GeV ensemble)
Dopant Depth (Simulated 90% localization)	< 1	nm	Ultra-shallow profile
Measured Dopant Depth (Tail)	8 ± 2	nm	Verified via Electron Beam Induced Etching (EBIE)
Annealing Temperature	950	°C	High vacuum (HV) post-irradiation treatment (2 hours)
SiV ZPL Wavelength	738	nm	Silicon-Vacancy center emission
GeV ZPL Wavelength	602	nm	Germanium-Vacancy center emission
SnV ZPL Wavelength	620	nm	Tin-Vacancy center emission
PbV ZPL Wavelength	550	nm	Lead-Vacancy center emission

Key Methodologies

The successful creation of ultra-shallow, site-selective color centers relies on precise control over the substrate quality, implantation parameters, and post-processing steps.

Substrate Preparation: CVD-grown electronic grade diamond (<1 ppb Nitrogen) was rigorously cleaned using hot (150 °C) Piranha Acid (H₂SO₄:H₂O₂ (30%) 2:1) to ensure an atomically clean surface prior to deposition.
Thin Film Deposition: Dopant precursors (Group IV elements) were deposited as 15-nm thin films using standard magnetron sputtering techniques.
Recoil Implantation: A dual beam FIB-SEM system utilizing a 30 keV Xe⁺ Focused Ion Beam (10 pA current) was used. The Xe⁺ beam was electrostatically scanned to pattern the thin film, transferring momentum to implant dopant atoms into the underlying diamond.
Chemical Stripping: Remaining thin films and residues were chemically stripped using sequential cycles of KOH, HCl, and Piranha Acid.
Defect Activation: Samples were annealed in a tube furnace under high vacuum (<2 x 10^-6 Torr) at 950 °C for 2 hours to promote the formation of the fluorescent vacancy complexes (e.g., SiV, GeV).
Depth Verification: The ultra-shallow depth profile was experimentally verified using Electron Beam Induced Etching (EBIE) in an environmental SEM, correlating the etch depth (AFM) with the Photoluminescence (PL) intensity.

6CCVD Solutions & Capabilities

The research demonstrates a powerful technique for quantum device engineering, but its success is fundamentally dependent on the quality of the diamond substrate. 6CCVD provides the necessary high-specification MPCVD diamond materials and customization services required to replicate and scale this advanced research.

Applicable Materials

To achieve the high quantum efficiency and coherence required for these Group IV color centers, researchers must utilize diamond with minimal intrinsic defects.

Research Requirement	6CCVD Material Solution	Rationale for Selection
Ultra-Low Defect Density	Electronic Grade Single Crystal Diamond (SCD)	Guaranteed sub-ppb nitrogen content, minimizing background NV centers and maximizing the coherence time of implanted Group IV defects.
Surface Integrity	Optical Grade SCD (Ra < 1 nm Polishing)	Essential for ultra-shallow implantation (< 1 nm depth). A superior surface finish reduces strain and minimizes scattering losses for integrated photonic devices.
High-Power Applications	High Thermal Conductivity SCD	Diamond’s superior thermal properties are critical for managing heat in integrated photonic circuits and high-density quantum arrays.

Customization Potential

6CCVD’s in-house manufacturing capabilities directly address the complex geometric and integration needs demonstrated in the paper (e.g., non-planar targets, integrated devices).

Paper Requirement / Application	6CCVD Customization Service	Benefit to Researcher
Wafer-Scale Processing	Custom Dimensions: Plates/wafers up to 125 mm (PCD) or large-area SCD.	Supports scaling from laboratory proof-of-concept to industrial-scale quantum chip fabrication.
Integrated Photonic Devices	Precision Polishing: SCD to Ra < 1 nm; Inch-size PCD to Ra < 5 nm.	Provides the low-loss surface necessary for fabricating high-quality photonic crystal cavities and waveguides adjacent to the implanted defects.
Electrical Contact Integration	Custom Metalization: Internal deposition of Au, Pt, Pd, Ti, W, Cu.	Enables the creation of electrodes or contact pads required for electrical readout or strain tuning of the implanted color centers.
Complex Geometries	Substrate Shaping: Custom thickness (0.1 µm to 10 mm) and laser cutting services.	Allows for the preparation of unique, non-planar substrates or micro-structures necessary for advanced integration, such as coupling to optical fibers or specialized resonators.

Engineering Support

6CCVD’s technical sales team, backed by our in-house PhD material scientists, offers authoritative support for optimizing the diamond substrate for specific implantation recipes. We understand the critical interplay between substrate purity, surface termination, and post-annealing treatments necessary to maximize color center yield and coherence.

We offer consultation on:

Selecting the optimal SCD grade based on target coherence time requirements.
Specifying surface orientation and termination for enhanced defect formation efficiency.
Designing custom substrate geometries for integrated [Quantum Photonic / Quantum Sensing] projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-020-18749-2