Dark defect charge dynamics in bulk chemical-vapor-deposition-grown diamonds probed via nitrogen vacancy centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-05-12 |
| Journal | Physical Review Materials |
| Authors | A Lozovoi, D. Daw, H. Jayakumar, C. A. Meriles, A Lozovoi |
| Institutions | City College of New York, The Graduate Center, CUNY |
| Citations | 13 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study identifies and characterizes a major, previously unnoticed point defect, referred to as âXâ, in bulk type-1b Chemical Vapor Deposition (CVD) diamond, which significantly impacts the stability of Nitrogen-Vacancy (NV) centers.
- Defect Discovery: A new, optically and magnetically dark point defect (âXâ) was revealed using advanced spin and charge dynamics protocols (DEER and PL excitation spectroscopy).
- High Abundance: Defect X concentration is found to be at least comparable to, or greater than, that of substitutional nitrogen (N0 or P1 centers), typically the most abundant impurity in CVD diamond.
- Deep Acceptor Level: Indirectly-detected photo-luminescence spectroscopy confirms that Defect X acts as a deep acceptor with an energy level approximately 1.6 eV above the valence band (VB).
- Charge Dynamics: The defect acts as a primary electron trap, facilitating electron tunneling from neutral substitutional nitrogen (N0) and influencing the critical NV-/NV0 charge state interconversion.
- Microscopic Hypothesis: While the exact atomic structure remains elusive, the defect is hypothesized to be a hydrogen-related complex (e.g., V-H), supported by Fourier-transformed infrared (FTIR) absorption data showing CH stretching modes.
- Engineering Relevance: Understanding this defect is mandatory for optimizing CVD diamond quality, particularly for applications relying on stable NV charge states, such as quantum computing and nanoscale sensing.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Defect X Acceptor Level | 1.6 | eV | Energy above Valence Band (VB) |
| Measured N0 (P1) Concentration | 0.25 ± 0.03 | ppm | Derived from DEER measurements |
| Nominal Nitrogen Concentration (CVD) | †1 | ppm | Manufacturer specification for type-1b diamond |
| NV Center Concentration | †10 | ppb | Calculated concentration (1 NV per 100 N impurities) |
| Average N Separation | 28 | nm | Calculated distance based on 0.25 ppm concentration |
| N0 Electron Tunneling Time (Ttun) | 2.4 ± 0.7 | ms | Characteristic time for N0 decay via tunneling to Defect X |
| NV T1 Relaxation Time | ~6 | ms | NV spin relaxation baseline (longer than Ttun) |
| NV- Recombination Time (Hole Capture) | 0.86 ± 0.09 | ms | Measured during green laser park protocol |
| NV- Ionization Recombination Time | 0.49 ± 0.05 | ms | Measured during red laser park protocol |
| Green Laser Wavelength | 532 | nm | Used for NV initialization and two-photon ionization |
| Red Laser Wavelength | 632 | nm | Used for NV recombination and direct ionization |
| IR Absorption Range (H-related) | 2800-3400 | cm-1 | Associated with CH stretching modes in the sample |
Key Methodologies
Section titled âKey MethodologiesâThe research relied on a combination of advanced optical and magnetic resonance techniques to probe the dark defect dynamics indirectly via the NV center.
- Material Preparation: Experiments were conducted on [100] type-1b CVD diamond crystals (3x3x0.1 mm3) with a nominal nitrogen concentration of †1 ppm and no post-growth treatment.
- Double Electron-Electron Resonance (DEER):
- N0 Quantification: The DEER protocol used the NV center as an optically-detected local spin probe (MW1) and synchronous microwave manipulation (MW2) of surrounding paramagnetic defects (N0). This measured inter-N0 dipolar couplings to derive the N0 concentration (0.25 ppm).
- Charge Dynamics Monitoring: An adapted DEER sequence introduced a variable wait time (Tw) after optical initialization (532 nm) to monitor the decay of N0 concentration, yielding the electron tunneling time (Ttun = 2.4 ms).
- NV Photo-Conversion Experiments:
- Charge State Mapping: Fluorescence microscopy was used to map the local NV- and NV0 charge states after selective green (532 nm) or red (632 nm) laser parking protocols.
- Recombination Rate Analysis: Measured NV- photoluminescence decay rates under green and red illumination protocols to infer differences in hole recapture efficiency, linking dynamics to the charge state of Defect X.
- Photo-Luminescence (PL) Excitation Spectroscopy:
- Defect X Level Determination: An infra-red (IR) laser beam (710-800 nm) was used during the park phase of the photo-conversion protocol. Local NVâNV0 conversion was observed even below the minimum two-step ionization energy (637 nm), indicating single-photon absorption from the valence band into the X acceptor level.
- Energy Level Calculation: Plotting the integrated NV- PL as a function of IR wavelength allowed the determination of the Defect X acceptor level at ~1.6 eV.
- Infrared Absorbance Spectroscopy: Fourier-transformed infrared (FTIR) measurements were performed on the samples, confirming the presence of hydrogen-related complexes via absorption bands associated with CH stretching modes (2800-3400 cm-1).
Commercial Applications
Section titled âCommercial ApplicationsâThe identification and characterization of Defect X are critical for improving the performance and reliability of diamond-based devices, particularly those relying on controlled charge states and carrier dynamics.
- Quantum Information Processing (QIP): Defect X acts as a major charge trap, causing instability in the NV- charge state. Mitigation of this defect is essential for achieving long coherence times and reliable initialization/readout in NV-based quantum memories and qubits.
- Nanoscale Sensing and Magnetometry: NV centers are widely used for high-resolution sensing. Charge state fluctuations (NV- â NV0) induced by Defect X introduce noise, limiting the sensitivity and operational stability of diamond quantum sensors.
- Power Electronics and Semiconductors: CVD diamond is a candidate for high-power devices due to its wide bandgap. Deep acceptor levels (1.6 eV) significantly influence carrier lifetime, mobility, and the overall performance and reliability of diamond semiconductor devices under high current injection.
- Optoelectronics and Photoconductivity: The defectâs role in trapping photo-generated electrons and holes dictates the materialâs photoconductive response, relevant for diamond-based photodetectors and UV/high-energy radiation sensors.
- CVD Growth Optimization: The findings provide specific targets for CVD growth engineers. Controlling hydrogen incorporation and minimizing the formation of this dark defect complex is necessary to produce high-quality, stable diamond material for advanced technological applications.
View Original Abstract
Although chemical vapor deposition (CVD) is one of the preferred routes to\nsynthetic diamond crystals, a full knowledge of the point defects produced\nduring growth is still incomplete. Here we exploit the charge and spin\nproperties of nitrogen-vacancy (NV) centers in type-1b CVD diamond to expose an\noptically and magnetically dark point defect, so far virtually unnoticed\ndespite an abundance comparable to (if not greater than) that of substitutional\nnitrogen. Indirectly-detected photo-luminescence spectroscopy indicates a donor\nstate 1.6 eV above the valence band, although the defectâs microscopic\nstructure and composition remain elusive. Our results may prove relevant to the\ngrowing set of applications that rely on CVD-grown single crystal diamond.\n
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2018 - Power Electronics Device Applications of Diamond Semiconductors