Scalable fabrication of coupled NV center - photonic crystal cavity systems by self-aligned N ion implantation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-04-06 |
| Journal | Optical Materials Express |
| Authors | Tim Schröder, Michael Walsh, Jiabao Zheng, Sara Mouradian, L. Li |
| Institutions | Brookhaven National Laboratory, SUNY Polytechnic Institute |
| Citations | 32 |
| Analysis | Full AI Review Included |
Technical Analysis and Material Sourcing Documentation: Scalable NV-PhC Systems
Section titled âTechnical Analysis and Material Sourcing Documentation: Scalable NV-PhC SystemsâReference: BNL-114306-2017-JA: Scalable fabrication of coupled NV center - photonic crystal cavity systems by self-aligned N ion implantation
This document translates the critical findings of the Brookhaven National Laboratory research into actionable technical specifications and highlights how 6CCVDâs advanced MPCVD diamond capabilities can facilitate and accelerate further research in scalable quantum photonics and diamond-based quantum memories.
Executive Summary
Section titled âExecutive Summaryâ- Core Breakthrough: Demonstration of a highly scalable, self-aligned lithography technique for integrating Nitrogen Vacancy (NV) centers directly into 2-D photonic crystal (PhC) cavities in single-crystal diamond (SCD).
- Scalability: The process enables the parallel fabrication of hundreds to thousands of coupled NV-cavity systems on a single chip, a crucial step for large-scale quantum integrated circuits.
- Performance Metrics: Achieved high-quality factors (Q up to ~8350) and unprecedented intensity enhancement factors ($F_{int}$) up to 93 ± 7, proving strong coupling efficacy.
- Localization Success: The self-aligned technique ensures spatial overlap between the NV defect and the cavity mode maximum with precision limited to a radius of ~42 nm, significantly improving coupling reliability compared to random creation.
- Targeted Defect Creation: Utilized 40 keV 15N ion implantation targeting a shallow depth of ~40 nm within a thin, high-purity SCD membrane (~200 nm).
- Spectral Control: Demonstrated spectral tuning of the cavity resonance via temperature variation, achieving a 5x Purcell enhancement of the narrow Zero-Phonon Line (ZPL) emission.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material | Single Crystal Diamond (SCD) | - | Required high purity for low background NV fluorescence. |
| SCD Thickness (Membrane) | ~200 | nm | Thin film optimized for Photonic Crystal fabrication. |
| Maximum Quality Factor (Q) | ~8350 | - | Achieved in L3 cavity, demonstrated spectral tuning ability. |
| Max Intensity Enhancement ($F_{int}$) | 93 ± 7 | x | Measured enhancement of the Phonon Sideband (PSB) emission. |
| Target NV Creation | 1.1 ± 0.2 | NVs/Cavity | Sample A, yielding ~37% probability of single-NV coupling. |
| Target Localization Precision | ~42 ± 13 | nm | Lateral radius of NV distribution around cavity maximum. |
| Ion Implantation Species | 15N | - | Used for controlled, targeted NV creation. |
| Ion Implantation Energy | 40 | keV | Set to minimize damage and target shallow depth. |
| Target Implantation Depth | ~40 | nm | Calculated range (SRIM) from the diamond surface. |
| Implantation Dose | 3 x 1012 | /cm2 | Low dose used to maintain low NV density. |
| Post-Implantation Annealing | 850 | °C | Required process to mobilize vacancies and form NV centers. |
| Cavity Design Types | L3 and M0 | - | Two 2-D photonic crystal lattice defect cavity designs tested. |
Key Methodologies
Section titled âKey MethodologiesâThe core achievement relies on a self-aligned lithography and implantation process using a single, high-aspect-ratio mask for both nanostructure patterning and 15N ion implantation.
- Hard Mask Preparation: A silicon-on-insulator (SOI) wafer was fabricated via standard processing to create a silicon hard mask (220 nm or 270 nm thick). This mask includes both the large photonic crystal features and the critical 20-35 nm diameter circular implantation apertures.
- Mask Placement: The prepared Si etch mask was carefully placed onto a high-purity, ~200 nm thick diamond membrane.
- Photonic Pattern Transfer (Etch Step 1): Oxygen Reactive Ion Etching (RIE) was used to transfer the photonic crystal pattern into the diamond. Due to the high aspect ratio of the mask features, the large photonic holes were etched through the membrane, but the smaller (aspect ratio ~4) implantation apertures remained protected.
- Targeted Ion Implantation (Defect Creation): 15N ions were implanted vertically at 40 keV energy, using the same Si mask as a physical shield. The ions passed only through the small implantation apertures, achieving precise spatial localization (~40 nm depth, ~42 nm lateral radius).
- Mask Removal: The Si mask was removed post-implantation.
- Annealing: The sample was annealed at 850 °C to promote vacancy migration and subsequent formation of the desired 15NV color centers.
- System Characterization: Photoluminescence (PL) and auto-correlation measurements confirmed high NV localization yield and quantified the coupling efficiency and quality factors.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the enabling diamond materials critical for successfully replicating and scaling up this complex quantum photonics fabrication scheme. The constraints of this researchâultra-thin membranes, high purity, precise alignment, and surface integrityâmap directly onto our advanced MPCVD fabrication expertise.
Applicable Materials
Section titled âApplicable MaterialsâThe foundation of this research is a high-quality, ultra-low background single-crystal diamond film.
- Optical Grade SCD (Low Nitrogen): To replicate the results and minimize spectral diffusion and decoherence, researchers require SCD with extremely low background nitrogen content (< 1 ppb). 6CCVD provides high-purity SCD wafers necessary to isolate the signal from the intentionally implanted 15NV centers.
- Thin Diamond Plates and Wafers: The experiment utilized a ~200 nm thick membrane. 6CCVD offers custom thickness SCD plates ranging from 0.1 ”m up to 500 ”m, allowing engineers to tailor the substrate thickness precisely for optimal PhC membrane fabrication yield and optical mode confinement.
| Material Requirement | 6CCVD Capability | Benefit to Quantum Research |
|---|---|---|
| Ultra-low N Impurities | Optical Grade SCD | Minimizes background fluorescence noise for clearer ZPL signal. |
| Thin Film Substrates | SCD 0.1 ”m - 500 ”m | Provides ideal starting material for membrane processing and high-Q cavity design. |
| Surface Preparation | Ra < 1 nm Polishing | Ensures defect-free surfaces crucial for subsequent high-resolution e-beam lithography and high Q factor attainment. |
Customization Potential
Section titled âCustomization PotentialâThe success of scalable fabrication relies on materials that accommodate multi-step nanoscale processing.
- Precision Sizing and Shaping: While the paper focuses on fabrication, subsequent integrated devices require chip-scale components. 6CCVD offers custom laser cutting and wafer sizing up to 125mm (PCD), ensuring materials fit standardized foundry tools.
- Integrated Metalization Services: For future steps toward tunable devices (e.g., using micro-electromechanical systems (MEMS) as suggested in the paperâs outlook), electrical contacts are necessary. 6CCVD offers in-house custom metalization (including Au, Pt, Pd, Ti, W, Cu) to simplify the integration of necessary biasing or tuning electrodes onto the diamond substrate.
- High-Q Surface Finish: The high Q factors achieved (up to ~8350) depend fundamentally on an extremely smooth surface finish. Our standard Ra < 1 nm polishing for SCD meets and exceeds the stringent requirements for nanophotonic device processing.
Engineering Support
Section titled âEngineering SupportâDeveloping scalable quantum memories based on NV centers is complex, requiring deep material and process knowledge.
- 6CCVDâs in-house PhD engineering team specializes in MPCVD diamond growth parameters, defect engineering, and material selection. We offer consultative support for projects focused on Spin-Photon Interfaces and Integrated Quantum Networks, helping researchers select the optimal material specifications (e.g., specific doping or low-nitrogen purity) required to replicate or extend high-performance NV center research.
- We facilitate global collaboration by offering DDU default shipping worldwide, with DDP available upon request, streamlining logistics for time-sensitive research projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Towards building large-scale integrated photonic systems for quantum information processing, spatial and spectral alignment of single quantum systems to photonic nanocavities is required. Here, we demonstrate spatially targeted implantation of nitrogen vacancy (NV) centers into the mode maximum of 2-d diamond photonic crystal cavities with quality factors up to 8000, achieving an average of 1:1 0:2 NVs per cavity. Nearly all NV-cavity systems have significant emission intensity enhancement, reaching a cavity-fed spectrally selective intensity enhancement, Fint, of up to 93. Although spatial NV-cavity overlap is nearly guaranteed within about 40 nm, spectral tuning of the NVâs zero-phonon-line (ZPL) is still necessary after fabrication. To demonstrate spectral control, we temperature tune a cavity into an NV ZPL, yielding FZPL int ~ 5 at cryogenic temperatures.