Generation of Tin-Vacancy Centers in Diamond via Shallow Ion Implantation and Subsequent Diamond Overgrowth
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-02-07 |
| Journal | Nano Letters |
| Authors | Alison E. Rugar, Haiyu Lu, Constantin Dory, Shuo Sun, Patrick J. McQuade |
| Institutions | SLAC National Accelerator Laboratory, Stanford University |
| Citations | 69 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research introduces the Shallow Ion Implantation and Growth (SIIG) method, a novel technique for generating high-quality, site-controlled Group-IV Tin-Vacancy (SnV-) centers in diamond.
- Core Value Proposition: SIIG overcomes the critical trade-off between precise site control (achieved via implantation) and high emitter quality (typically achieved via synthesis/HPHT).
- Methodology: Utilizes extremely low-energy (1 keV) Sn ion implantation through a thin PMMA mask, followed immediately by microwave-plasma Chemical Vapor Deposition (MPCVD) diamond overgrowth.
- Quality Improvement: The subsequent CVD growth heals lattice damage and incorporates Sn atoms into the SnV- structure, resulting in clean bulk photoluminescence (PL) spectra free of extraneous defect peaks (631 nm and 647 nm).
- Site Control: Demonstrated precise site-controlled generation with a 78% yield (at least one SnV- center per hole) in 30 nm patterned arrays.
- Reduced Broadening: Optimized SIIG samples (Sample C) exhibit narrow inhomogeneous broadening (approximately 100 GHz), which is narrow enough for strain-tuning techniques required for quantum applications.
- Compatibility: The method uses standard MPCVD growth conditions for pure diamond, making it highly compatible with existing diamond nanophotonic device fabrication techniques.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Implantation Energy (Shallow) | 1 | keV | SIIG method (Sample B/C) |
| Implantation Energy (Baseline) | 370 | keV | Vacuum Anneal (Sample A) |
| Implantation Dose | 2 x 1013 | cm-2 | Used for all samples |
| Ion Localization Depth (SRIM) | ~2 | nm | Depth of Sn ions after 1 keV implantation |
| Lateral/Longitudinal Straggle (SRIM) | 3 | Angstrom | Calculated straggle for 1 keV Sn+ |
| PMMA Mask Thickness | ~50 | nm | Used to stop 1 keV ions |
| MPCVD Overgrowth Thickness | 90 | nm | Nominal thickness grown on Sample B |
| SnV- Zero-Phonon Line (ZPL) | ~620 | nm | Characteristic emission wavelength |
| Inhomogeneous Broadening (Sample A, C transition) | 263 ± 5 | GHz | Baseline (Implanted/Vacuum Annealed) |
| Inhomogeneous Broadening (Sample C, C transition) | 101 ± 1 | GHz | Optimized SIIG result |
| Site Control Yield | 78 | % | Percentage of 30 nm holes yielding >= 1 SnV- center |
| Conversion Efficiency Estimate | >1 | % | Estimated for patterned array |
| Vacuum Anneal Temperature (Sample A) | 800 / 1100 | °C | Two stages, 30 minutes each |
| MPCVD Stage Temperature | 650 | °C | Diamond overgrowth temperature |
| MPCVD Pressure | 23 | Torr | Diamond overgrowth pressure |
Key Methodologies
Section titled âKey MethodologiesâThe SIIG method (Shallow Ion Implantation and Growth) applied to Sample B involved the following sequential steps:
-
Initial Preparation:
- Clean electronic grade diamond plate using a boiling tri-acid solution (1:1:1 sulfuric:nitric:perchloric acids).
- Remove 500 nm of diamond via O2 plasma etch.
-
Mask Fabrication:
- Spin-coat a thin layer (~50 nm) of poly(methyl methacrylate) (PMMA, 950 PMMA A2).
- Pattern arrays of square holes (20 nm to 150 nm side length) using electron-beam (e-beam) lithography.
- Develop the PMMA mask in a 5°C 3:1 solution of isopropanol:water.
-
Shallow Ion Implantation:
- Implant 120Sn+ ions at a low energy of 1 keV.
- Implantation dose was 2 x 1013 cm-2.
-
Surface Preparation for Growth:
- Remove the PMMA mask using Remover PG.
- Clean the diamond surface using H2 plasma to remove unwanted sp2-bonded carbon resulting from implantation damage.
-
Diamond Overgrowth (MPCVD):
- Immediately grow a nominally 90-nm thick layer of diamond using Microwave-Plasma CVD (Seki Diamond Systems SDS 5010).
- Gas Flows: H2 at 300 sccm; CH4 at 0.5 sccm.
- Conditions: Stage temperature 650°C; Microwave power 1100 W; Pressure 23 Torr.
- Mechanism: The growth process heals the damaged lattice and incorporates the shallowly implanted Sn atoms into the growing sp3 lattice to form SnV- centers.
Commercial Applications
Section titled âCommercial ApplicationsâThe SIIG method provides a scalable, high-quality manufacturing route for quantum emitters, addressing key challenges in integrating solid-state spin qubits into functional devices.
- Quantum Network Nodes: SnV- centers are highly promising solid-state spin qubits due to their long spin coherence times without requiring dilution refrigeration, making them ideal candidates for quantum memory and repeater nodes.
- Integrated Nanophotonics: The high-precision, site-controlled placement of emitters is essential for coupling them efficiently to nanophotonic structures (e.g., diamond microdisks, photonic crystal cavities) for enhanced photon collection and quantum-optical interfaces.
- Scalable Quantum Device Fabrication: SIIG is compatible with existing diamond fabrication techniques (etching, inverse design) and uses standard CVD growth parameters, enabling the mass production of quantum chips and arrays.
- Quantum Sensing: High-quality, low-strain SnV- centers can be used as sensitive probes for electric and magnetic fields in diamond-based quantum sensors.
- New Material Discovery: The versatility of SIIGâusing low-damage implantation followed by growthâcan be extended beyond diamond and SnV- to accelerate the discovery and optimization of new color centers in various host materials (e.g., Lead-related emitters).
View Original Abstract
Group IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. The future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV<sup>-</sup>) center, conventional site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV<sup>-</sup> centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.