Photo‐Induced Charge State Dynamics of the Neutral and Negatively Charged Silicon Vacancy Centers in Room‐Temperature Diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-03-12 |
| Journal | Advanced Science |
| Authors | G. Garcia‐Arellano, Gabriel I. López‐Morales, Neil B. Manson, Johannes Flick, A. A. Wood |
| Institutions | City College of New York, The Graduate Center, CUNY |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research provides a unified, microscopic understanding of the photo-induced charge state dynamics of Silicon Vacancy (SiV) centers in Chemical Vapor Deposition (CVD) diamond at room temperature, critical for quantum technology development.
- Charge State Control: Demonstrated robust, room-temperature control over the interconversion between the neutral (SiVº), single-negative (SiV-), and double-negative (SiV2-) charge states using multi-color infrared (IR) excitation.
- SiVº Recombination Mechanism: The conversion of SiVº to SiV- is confirmed as a single-photon process. The rate exhibits a linear dependence on laser power, corresponding to the optical injection of an electron from the diamond Valence Band Maximum (VBM).
- SiV- Recombination Mechanism: The conversion of SiV- to the optically dark SiV2- state is driven by a photo-activated electron tunneling process originating from proximal substitutional nitrogen (Nº) impurities.
- Non-Exponential Decay: The SiV- decay is non-exponential and fractional, successfully modeled using rate equations that account for the varying distances between the SiV center and its nearest-neighbor Nº donor.
- DFT Validation: Density Functional Theory (DFT) calculations validate the energetics, showing that the tunneling electron originates from delocalized intra-valence-band orbitals (HOMO-1, HOMO-2) of the Nº center, rather than the deep Nº donor level itself.
- Engineering Implication: The findings highlight the necessity of reducing proximal donor concentrations to stabilize SiV centers and minimize charge blinking, crucial for high-fidelity quantum applications.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Host Material | CVD Diamond | N/A | [100] orientation, measured 5-10 µm below surface |
| Nitrogen (N) Concentration | 3 | ppm | Substitutional impurity concentration in sample |
| SiV Concentration | ~0.3 | ppm | Estimated concentration |
| NV Concentration | ~0.03 | ppm | Estimated concentration |
| SiV- ZPL Detection | 737 | nm | Zero Phonon Line used for fluorescence readout |
| IR Excitation Range | 720-874 | nm | Wavelength range for charge state interconversion |
| SiVº → SiV- Activation Energy | 1.53(5) | eV | Threshold for electron injection from Valence Band |
| SiVº Relaxation Energy (ΔE) | 74 | meV | Energy dissipated due to SiV relaxation after ionization |
| SiVº Atomic Reconfiguration (ΔQ) | 0.21 | amu1/2 A | Small change, suggesting weak phonon coupling |
| N-mediated Tunneling Radius (r0) | 1 | nm | Effective radius used in the SiV- to SiV2- tunneling model |
| DFT Functional Used | HSE06 | N/A | Used for calculating charge state transition levels |
| Supercell Size (DFT) | 512, 2474 | atoms | Used for energetics and wavefunction analysis |
Key Methodologies
Section titled “Key Methodologies”The study utilized a multi-color scanning confocal microscope combined with Density Functional Theory (DFT) modeling to characterize charge dynamics under ambient conditions.
- Sample and Setup: Experiments were performed on a [100] CVD diamond sample (3 ppm N) using 532 nm (green), 632 nm (red), and a tunable continuous wave (cw) Ti:Sa laser (700-1000 nm, IR).
- SiV- Initialization: A 532 nm laser scan (5 mW) was used to establish an SiV- rich background across the measurement plane.
- SiVº Generation: The 532 nm laser was parked for 3 s to generate an SiVº-rich “dark halo” via preferential hole capture from remote NV centers.
- IR Charge Cycling Protocol: The tunable IR laser was parked sequentially at two distinct locations:
- Site X (SiVº-rich): Measured SiVº recombination (SiVº → SiV-) by observing the growth of SiV- fluorescence.
- Site Y (SiV- rich): Measured SiV- recombination (SiV- → SiV2-) by observing the decay of SiV- fluorescence.
- Recombination Rate Analysis: The SiVº recombination rate (ξ0) was extracted from exponential fits and plotted against IR laser power (PIR) to confirm single-photon dynamics and determine the 1.53 eV activation threshold.
- Tunneling Model Application: The non-exponential decay of SiV- fluorescence was fitted using a rate equation model incorporating electron tunneling from proximal Nº impurities, averaged over the nearest-neighbor probability distribution (g(r)).
- DFT Modeling: DFT calculations (HSE06 functional) were performed on SiV and N centers to map thermodynamic charge-state transition levels, determine adiabatic potential energy surfaces (PES), and analyze the spatial characteristics of the electronic wave functions (HOMO-1, HOMO-2) responsible for tunneling.
Commercial Applications
Section titled “Commercial Applications”The precise control and understanding of SiV charge state dynamics are vital for advancing diamond-based quantum technologies.
- Quantum Information Processing (QIP): SiV centers are key components in photonic quantum networks. The ability to reliably initialize and stabilize the SiVº state (which offers superior spin coherence and narrow ZPL) is essential for high-fidelity qubit operation and entanglement generation.
- Nanoscale Quantum Sensing: Charge state stability directly impacts the performance of SiV-based sensors. Minimizing charge blinking (the SiV- ↔ SiV2- transition) by controlling proximal nitrogen is necessary for achieving long measurement times and high sensitivity at ambient temperatures.
- Single-Photon Sources (SPS): The SiVº state is a promising SPS candidate. This research provides the necessary materials engineering guidelines (e.g., low N concentration, controlled Fermi level) to produce stable, high-purity SiVº emitters for integrated photonic circuits.
- Photoelectric Diamond Devices: The detailed mechanisms of carrier injection (VBM injection for SiVº) and impurity-mediated transfer (N tunneling for SiV-) inform the design of optimized diamond photodetectors and photoconductivity devices, particularly concerning the management of silicon and nitrogen defects.
- Advanced Materials Engineering: Provides feedback for CVD diamond manufacturers (like 6ccvd.com) on optimizing growth recipes to control impurity profiles (N and Si) and defect proximity, ensuring the production of quantum-grade diamond substrates with stable, high-performance color centers.
View Original Abstract
Abstract The silicon vacancy (SiV) center in diamond is drawing much attention due to its optical and spin properties, attractive for quantum information processing and sensing. Comparatively little is known, however, about the dynamics governing SiV charge state interconversion mainly due to challenges associated with generating, stabilizing, and characterizing all possible charge states, particularly at room temperature. Here, multi‐color confocal microscopy and density functional theory are used to examine photo‐induced SiV recombination — from neutral, to single‐, to double‐negatively charged — over a broad spectral window in chemical‐vapor‐deposition (CVD) diamond under ambient conditions. For the SiV 0 to SiV ‐ transition, a linear growth of the photo‐recombination rate with laser power at all observed wavelengths is found, a hallmark of single photon dynamics. Laser excitation of SiV ‒ , on the other hand, yields only fractional recombination into SiV 2‒ , a finding that is interpreted in terms of a photo‐activated electron tunneling process from proximal nitrogen atoms.