Surprising stability of neutral interstitial hydrogen in diamond and cubic BN
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-01-21 |
| Journal | Journal of Physics Condensed Matter |
| Authors | John L. Lyons, Chris G. Van de Walle |
| Institutions | University of California, Santa Barbara |
| Citations | 9 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Interstitial Hydrogen in Diamond
Section titled âTechnical Documentation & Analysis: Interstitial Hydrogen in DiamondâReference Paper: Lyons, JL, Van de Walle, CG. (2016). Surprising stability of neutral interstitial hydrogen in diamond and cubic BN. JOURNAL OF PHYSICS-CONDENSED MATTER, 28(6).
Executive Summary
Section titled âExecutive SummaryâThis theoretical analysis, highly relevant to MPCVD diamond growth and quantum applications, confirms the unique behavior of interstitial hydrogen ($\text{H}_i$) in diamond. 6CCVD provides the high-purity, custom-engineered Single Crystal Diamond (SCD) required to experimentally validate and leverage these findings.
- Positive-U Behavior Confirmed: $\text{H}_i$ in diamond exhibits strong positive-U character (U = 2.03 eV), a behavior fundamentally different from the negative-U character observed in most other wide-band-gap semiconductors (e.g., GaN, AlN).
- Neutral State Stability: The neutral charge state ($\text{H}_i^0$) is predicted to be stable over an exceptionally wide Fermi-level range of 2.03 eV, indicating its persistence across various doping conditions.
- CVD Relevance: Hydrogen is a common unintentional impurity in Chemical Vapor Deposition (CVD) diamond growth. Understanding its charge state stability is critical for controlling material quality and electronic properties.
- NV Center Impact: The findings directly impact the formation kinetics and charge state stability of the Nitrogen-Vacancy (NV) center, a key defect for quantum computing, spintronics, and metrology applications.
- Structural Preference: $\text{H}_i$ strongly prefers the Bond-Centered (BC) configuration, leading to significant lattice relaxation, which is attributed to diamondâs small lattice constant.
- Computational Accuracy: Calculations utilized state-of-the-art Hybrid Density Functional Theory (HSE) to achieve high accuracy, predicting a band gap (5.35 eV) in close agreement with the experimental value (5.47 eV).
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the HSE calculations regarding bulk diamond properties and $\text{H}_i$ defect levels.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Calculated Lattice Constant | 3.54 | Ă | Diamond bulk property (Exp: 3.57 Ă ) |
| Calculated Indirect Band Gap | 5.35 | eV | HSE calculation (Exp: 5.47 eV) |
| Calculated Direct Band Gap ($\Gamma$) | 7.06 | eV | HSE calculation (Exp: 7.02 eV) |
| $\text{H}_i$ Positive-U Value (U) | 2.03 | eV | Defined as the energy difference between (+/0) and (0/-) transition levels |
| $\text{H}_i$ Stability Range ($\text{H}_i^0$) | 2.03 | eV | Fermi-level range where the neutral state is most stable |
| $\text{H}_i$ Transition Level (+/0) | 1.76 | eV | Above Valence Band Maximum (VBM) |
| $\text{H}_i$ Transition Level (0/-) | 3.79 | eV | Above Valence Band Maximum (VBM) |
| $\text{H}_i$ Transition Level (+/-) | 2.78 | eV | Above VBM (Used for universal band alignment reference) |
| $\text{H}_i$ Exchange Splitting ($\text{H}_i^0$) | 2.52 | eV | Calculated for the neutral charge state |
| $\text{H}_i$ Metastable Energy (Tetrahedral) | 1.20 | eV | Higher than the preferred Bond-Centered (BC) configuration |
Key Methodologies
Section titled âKey MethodologiesâThe theoretical results rely on a highly specific computational recipe using advanced Density Functional Theory (DFT). Experimental validation of these defect levels requires diamond materials grown under controlled MPCVD conditions, which 6CCVD specializes in.
- Computational Method: Generalized Kohn-Sham scheme utilizing the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional.
- Supercell Geometry: Defect calculations performed using a 216-atom supercell to minimize spurious defect-defect interactions.
- Kinetic Energy Cutoff: A high cutoff of 400 eV was applied to ensure convergence and accuracy.
- Brillouin Zone Sampling: A 2x2x2 special k-point mesh was used for sampling the Brillouin zone.
- HSE Functional Parameters: The HSE mixing parameter ($\alpha$) was set to 0.25, and the screening length ($\omega^{-1}$) was set to 0.2 Ă .
- Energy Reference: Formation energies were calculated relative to the energy of one-half the $\text{H}_2$ dimer, a standard reference for hydrogen chemical potential.
- Correction: Finite-size supercell corrections were applied to accurately model charged defect states.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical role of hydrogen impurities in CVD diamond, particularly concerning NV center formation and charge state control. 6CCVD provides the necessary high-purity, custom-engineered diamond substrates to experimentally verify these theoretical predictions and advance quantum device fabrication.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and Extensionâ| Research Requirement | 6CCVD Material Solution | Technical Rationale |
|---|---|---|
| Intrinsic Defect Study | High Purity Single Crystal Diamond (SCD) | Required for fundamental studies of $\text{H}_i$ stability, minimizing interference from other unintentional impurities (e.g., Nitrogen). |
| NV Center Research | Controlled Nitrogen-Doped SCD | Essential for studying the interaction between $\text{H}_i$ and NV centers, as discussed in the paper. 6CCVD offers precise nitrogen incorporation during MPCVD growth. |
| Electronic Control | Boron-Doped Diamond (BDD) Plates | To experimentally shift the Fermi level ($\text{E}_F$) across the predicted 2.03 eV stability range of $\text{H}_i^0$, controlled p-type doping is necessary. |
Customization Potential for Advanced Research
Section titled âCustomization Potential for Advanced Researchâ6CCVDâs in-house manufacturing capabilities directly address the needs of researchers working on diamond defects and quantum applications:
- Custom Dimensions: We supply SCD and PCD plates/wafers up to 125mm in diameter, allowing for large-scale experimental arrays or device fabrication.
- Thickness Control: Precise control over active layer thickness is available, ranging from 0.1 ”m to 500 ”m (SCD/PCD), and substrate thicknesses up to 10 mm.
- Surface Engineering: For high-fidelity optical and electronic measurements (critical for NV centers), 6CCVD offers ultra-smooth polishing:
- SCD: Surface roughness $\text{R}_a$ < 1 nm.
- Inch-size PCD: Surface roughness $\text{R}_a$ < 5 nm.
- Metalization Services: If subsequent device fabrication requires ohmic contacts or gate structures, 6CCVD provides custom metalization stacks (Au, Pt, Pd, Ti, W, Cu) applied directly to the diamond surface.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the physics and chemistry of MPCVD diamond growth and defect engineering. We offer consultation services to assist researchers in:
- Material Selection: Choosing the optimal diamond grade (e.g., high-purity SCD vs. controlled-doped BDD) to achieve specific Fermi-level positions necessary to probe the predicted $\text{H}_i$ charge states.
- Growth Recipe Optimization: Tailoring CVD parameters to minimize or intentionally incorporate hydrogen impurities, crucial for controlling NV center formation kinetics.
- Surface Termination: Advising on surface preparation (e.g., hydrogen termination, which affects the VBM position) to align with specific experimental requirements derived from theoretical models.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In virtually all semiconductors and insulators, hydrogen interstitials ([Formula: see text]) act as negative-U centers, implying that hydrogen is never stable in the neutral charge state. Using hybrid density functional calculations, we find a different behavior for [Formula: see text] in diamond and cubic BN. In diamond, [Formula: see text] is a very strong positive-U center, and the [Formula: see text] charge state is stable over a Fermi-level range of more than 2 eV. In cubic BN, a III-V compound similar to diamond, we also find positive-U behavior, though over a much smaller Fermi-level range. These results highlight the unique behavior of [Formula: see text] in these covalent wide-band-gap semiconductors.