Narrow-Linewidth Tin-Vacancy Centers in a Diamond Waveguide

At a Glance

Metadata	Details
Publication Date	2020-08-03
Journal	ACS Photonics
Authors	Alison E. Rugar, Constantin Dory, Shahriar Aghaeimeibodi, Haiyu Lu, Shuo Sun
Institutions	Stanford University, SLAC National Accelerator Laboratory
Citations	58
Analysis	Full AI Review Included

Technical Documentation & Analysis: Narrow-Linewidth SnV Centers in Diamond Waveguides

This document analyzes the research paper “Narrow-linewidth tin-vacancy centers in a diamond waveguide” (arXiv:2005.10385v2) to provide technical specifications and highlight how 6CCVD’s specialized Microwave Plasma Chemical Vapor Deposition (MPCVD) diamond materials and processing capabilities can support and advance this critical quantum photonics research.

Executive Summary

The research successfully demonstrates the integration of high-quality, narrow-linewidth tin-vacancy (SnV^-) quantum emitters into suspended diamond nanophotonic waveguides, a crucial step toward scalable quantum processors.

First Integration: Achieved the first successful coupling of SnV^- centers to a nanophotonic waveguide, a fundamental building block for waveguide quantum electrodynamics.
High Coherence: Measured extremely narrow optical linewidths, achieving 29 ± 5 MHz and 36 ± 2 MHz, comparable to previously reported lifetime-limited performance.
Advanced Method: Utilized the Shallow Ion Implantation and Growth (SIIG) method, combining low-energy ¹²⁰Sn⁺ implantation with subsequent MPCVD diamond overgrowth (90 nm).
Material Requirement: Requires high-purity, electronic grade Single Crystal Diamond (SCD) for both the substrate and the high-quality overgrowth layer.
Fabrication Complexity: Waveguides were fabricated using advanced quasi-isotropic etching techniques to create suspended nanobeam structures (400 nm wide, 280 nm thick).
Quantum Advantage: Confirms SnV^- as a promising qubit candidate capable of operating at higher temperatures (> 1 K) compared to SiV^- centers, simplifying cryogenic requirements.

Technical Specifications

The following hard data points were extracted from the experimental results and methodology:

Parameter	Value	Unit	Context
Emitter Type	SnV^-	N/A	Negatively charged Tin-Vacancy center
Implantation Ion	¹²⁰Sn⁺	N/A	Used for Shallow Ion Implantation (SIIG)
Implantation Energy	1	keV	Low energy required for shallow embedding
Implantation Dose	1.6 x 10¹⁰	cm^-2	Low dose for single-emitter isolation
MPCVD Overgrowth Thickness	90	nm	Diamond layer grown immediately after implantation
Waveguide Width	400	nm	Final dimension of suspended nanobeam
Waveguide Thickness	280	nm	Final dimension of suspended nanobeam
Minimum Linewidth (PLE)	29 ± 5	MHz	Measured via Lorentzian fit (Top-Down configuration)
Average Linewidth	36 ± 3	MHz	Average reproducibility across multiple SnV^- centers
Operating Temperature (PLE)	1.7	K	Required for narrow-linewidth characterization
Spectral Diffusion FWHM	~130	MHz	Measured instability under 50 nW excitation

Key Methodologies

The successful integration relies heavily on precise material preparation and advanced MPCVD growth techniques:

Substrate Preparation: Electronic grade diamond chip was cleaned via boiling tri-acid solution (nitric, sulfuric, perchloric acids) and the top ~500 nm was removed via O₂ plasma etch.
Shallow Ion Implantation: ¹²⁰Sn⁺ ions were implanted at 1 keV and a dose of 1.6 x 10¹⁰ cm^-2.
MPCVD Overgrowth (SIIG): The implanted chip was cleaned with H₂ plasma immediately before 90 nm of diamond was grown via Microwave-Plasma Chemical Vapor Deposition (MPCVD). This embeds the SnV^- centers 90 nm below the surface.
Etch Mask Deposition: 200 nm of Si_xN_y was grown via PECVD to serve as the primary etch mask.
Patterning: Electron-beam lithography (FOx-16) and RIE (SF₆, CH₄, N₂) were used to transfer the waveguide pattern into the Si_xN_y mask.
Anisotropic Etch: An anisotropic O₂ RIE was performed to etch the diamond structure.
Quasi-Isotropic Undercut: A high-temperature O₂ RIE step, performed with the forward bias turned off and high Inductively Coupled Plasma (ICP) power, was used to preferentially etch along the {110} planes, releasing the suspended nanobeam waveguides.
Mask Removal: Final cleaning in hydrofluoric acid (HF) removed the Si_xN_y and Al₂O₃ etch masks.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality SCD materials and specialized processing required to replicate and extend this cutting-edge quantum photonics research. Our expertise in MPCVD growth and precision fabrication directly addresses the critical material requirements of the SIIG method.

Applicable Materials

To achieve the narrow linewidths and high-quality nanostructures demonstrated, the research requires ultra-pure diamond.

Research Requirement	6CCVD Solution & Material	Technical Advantage
Starting Substrate	Optical Grade Single Crystal Diamond (SCD)	Ultra-low nitrogen content (PPM level) is essential for minimizing strain and charge noise, ensuring long spin coherence times for SnV^- centers.
Color Center Generation	Custom MPCVD Overgrowth Service	We specialize in MPCVD growth, providing the precise 90 nm epitaxial layer required for the Shallow Ion Implantation and Growth (SIIG) method. This ensures optimal embedding depth (90 nm) and high crystal quality around the implanted Sn ions.
Future Integration	Boron-Doped Diamond (BDD)	For future electro-mechanically controlled waveguides (as suggested in the paper’s conclusion), BDD films can be supplied for integrated electrodes or charge stabilization layers.

Customization Potential

The fabrication of suspended nanobeams requires exceptional dimensional control and surface quality, areas where 6CCVD excels.

Precision Thickness Control: The resulting waveguides are 280 nm thick. 6CCVD offers custom thinning and polishing services for SCD films down to 0.1 µm thickness, ensuring the precise dimensional control necessary for high-performance nanophotonic devices.
Ultra-Smooth Polishing: The quasi-isotropic etch relies on high-quality starting surfaces. 6CCVD guarantees SCD polishing with surface roughness Ra < 1 nm, minimizing scattering losses in the final waveguide structures.
Large-Scale Processing: While the paper used a 2 x 2 mm² chip, 6CCVD can supply SCD plates and PCD wafers up to 125mm in diameter, enabling the scaling required for “large-scale quantum photonic processors.”
Metalization for Deterministic Placement: The paper notes that deterministic positioning of SnV^- centers is essential for future superradiance experiments. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) crucial for defining implantation masks via lithography or for fabricating integrated electrodes for charge stabilization (as suggested by Ref. 35).

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD growth parameters and material optimization for quantum applications. We can assist researchers in optimizing the SIIG process by tailoring the overgrowth layer quality (e.g., controlling residual strain and impurity incorporation) to mitigate issues like spectral diffusion and blinking observed in the SnV^- centers.

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

View Original Abstract

Integrating solid-state quantum emitters with photonic circuits is essential for realizing large-scale quantum photonic processors. Negatively charged tin-vacancy (SnV$^-$) centers in diamond have emerged as promising candidates for quantum emitters because of their excellent optical and spin properties including narrow-linewidth emission and long spin coherence times. SnV$^-$ centers need to be incorporated in optical waveguides for efficient on-chip routing of the photons they generate. However, such integration has yet to be realized. In this Letter, we demonstrate the coupling of SnV$^-$ centers to a nanophotonic waveguide. We realize this device by leveraging our recently developed shallow ion implantation and growth method for generation of high-quality SnV$^-$ centers and the advanced quasi-isotropic diamond fabrication technique. We confirm the compatibility and robustness of these techniques through successful coupling of narrow-linewidth SnV$^-$ centers (as narrow as $36\pm2$ MHz) to the diamond waveguide. Furthermore, we investigate the stability of waveguide-coupled SnV$^-$ centers under resonant excitation. Our results are an important step toward SnV$^-$-based on-chip spin-photon interfaces, single-photon nonlinearity, and photon-mediated spin interactions.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acsphotonics.0c00833