Nitrogen-related point defects in homoepitaxial diamond (001) freestanding single crystals
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-04-24 |
| Journal | Journal of Applied Physics |
| Authors | Tokuyuki Teraji, Chikara Shinei |
| Institutions | National Institute for Materials Science |
| Citations | 19 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study successfully demonstrated precise control over nitrogen doping and defect charge states in high-purity, homoepitaxial diamond grown by Microwave Plasma Chemical Vapor Deposition (MPCVD).
- Doping Control: Nitrogen concentration was successfully controlled across a wide range, from 10 ppb to 10 ppm, by adjusting the N/C gas ratio.
- High Uniformity: Nitrogen incorporation was highly uniform throughout the crystal, with a standard deviation (SD) consistently measured at less than 10% of the average concentration.
- Defect Structure: The majority of incorporated nitrogen (approximately 70%) exists as neutral substitutional nitrogen (Ns0), which acts as the necessary donor for forming negatively charged NV centers.
- Quantum Sensor Optimization: The NV centers (NV-) and NVH centers (NVH-) were found to be predominantly negatively charged (approximately 90% of total NV), which is the required state for high-sensitivity quantum magnetic sensing.
- Incorporation Efficiency: The nitrogen incorporation efficiency (ratio of crystal [N] to gas N/C ratio) was determined to be constant across the tested range, averaging (1.9 ± 0.2) x 10-4.
- Crystal Quality: The use of oxygen-adding growth conditions suppressed the formation of non-epitaxial crystallites and growth hillocks, maintaining high crystalline quality even at high nitrogen doping levels.
- Hydrogen Presence: Hydrogen was incorporated into the crystal at concentrations roughly equivalent to the nitrogen concentration, although less than 10% of this hydrogen was found in the form of NVH centers.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nitrogen Doping Range | 10 ppb to 10 ppm | N/C gas ratio | Achieved control range in diamond crystal. |
| Nitrogen Uniformity (SD) | < 10% | % | Standard deviation relative to average [N] concentration. |
| Nitrogen Incorporation Efficiency | (1.9 ± 0.2) x 10-4 | Unitless | Ratio of crystal [N] to gas N/C ratio. |
| Substitutional Nitrogen (Ns0) Fraction | ~70% | % | Fraction of total nitrogen in the neutral charge state (P1 center). |
| Charged Substitutional Nitrogen (Ns+) Fraction | 20-30% | % | Indicates presence of acceptor defects. |
| NV- Fraction of Total NV | ~90% | % | Negatively charged NV centers, optimal for quantum sensing. |
| NVH Concentration | < 5% | % | Relative to total nitrogen concentration. |
| Hydrogen Concentration [H] | 1.5-4 times higher | Ratio | Relative to nitrogen concentration [N] (SIMS data). |
| Carbon Isotope Enrichment (Source Gas) | >99.9% | 12C | Methane source gas purity. |
| Carbon Isotope Enrichment (Diamond Crystal) | 99.96% | 12C | Measured concentration in the grown film (SIMS). |
| Ns0 Conversion Coefficient (FTIR) | 261,000 | ppm cm | For absorption peak at 1344 cm-1. |
| Ns+ Conversion Coefficient (FTIR) | 38,800 | ppm cm | For absorption peak at 1332 cm-1. |
Key Methodologies
Section titled âKey MethodologiesâThe homoepitaxial diamond films were grown using a microwave-plasma CVD (MPCVD) system under highly controlled conditions, incorporating isotopic enrichment and oxygen addition.
- Growth System: Microwave-plasma CVD system (NIMS).
- Substrate: HPHT-grown Type-Ib (100) diamond substrates (3.5 x 3.5 mm2 area, 1 mm thickness).
- Source Gases & Purity:
- Carbon Source: 12C isotopically enriched methane (CH4, purity 8N, >99.9% 12C).
- Nitrogen Dopant: 15N2 gas (purity >3N, 98% 15N enrichment).
- Carrier Gas: Hydrogen (H2, purity 9N, palladium purified).
- Additive Gas: Oxygen (O2, purity 6N5).
- CVD Growth Parameters (Standard):
- Reaction Pressure: 110 Torr.
- Microwave Power: 1.4 kW (except Sample 4 at 1.7 kW).
- Methane Concentration (CH4/Total Gas): 10%.
- Oxygen Concentration (O2/Total Gas): 2%.
- Substrate Temperature: 1020-1090 °C.
- Doping Range (N/C Gas Ratio): 20,000 ppm to 80,000 ppm (for 15N-doped samples).
- Characterization Techniques:
- Impurity Concentration & Depth Profile: Secondary Ion Mass Spectrometry (SIMS).
- Substitutional Nitrogen (Ns0) & NVH-: Electron Paramagnetic Resonance (EPR).
- Charge States (Ns0, Ns+, NVH0): Fourier Transform Infrared Spectroscopy (FTIR).
- NV Charge States (NV-, NV0): Photoluminescence (PL) spectroscopy.
Commercial Applications
Section titled âCommercial ApplicationsâThe precise control of nitrogen doping and the resulting high concentration of negatively charged NV centers (NV-) in high-purity, isotopically enriched diamond directly targets several high-value engineering and commercial sectors.
| Application Area | Relevance to Research Findings |
|---|---|
| Quantum Sensing & Metrology | The ability to create high-density, uniform NV- centers in 12C-enriched diamond (which maximizes coherence time T2) is foundational for developing highly sensitive magnetic field, electric field, and temperature sensors. |
| Quantum Computing | NV centers serve as solid-state qubits. Precise control over their concentration and charge state is necessary for scaling up quantum registers and creating reliable quantum memory devices. |
| High-Purity Diamond Substrates | The use of oxygen-adding CVD conditions to suppress defects and maintain high crystallinity is crucial for producing high-quality, free-standing diamond substrates for advanced electronics. |
| High-Power Electronics | High-purity, low-defect diamond is an excellent heat spreader and semiconductor material. Controlled doping allows for the creation of specific device layers (e.g., for Schottky diodes or MOSFETs). |
| Isotope Engineering | The successful incorporation of 15N and high enrichment of 12C demonstrates advanced isotope control, which is vital for optimizing spin properties and reducing decoherence in quantum devices. |
View Original Abstract
Controllability of nitrogen doping, types of nitrogen-related defects, and their charge states in homoepitaxial diamond (001) crystals were investigated. For these purposes, 15N-doped 12C-enriched free-standing chemical vapor deposited diamond (001) crystals were grown through long-time growth using 12C-enriched methane as the carbon source gas and 15N-enriched molecular nitrogen as the nitrogen source gas. The formation of non-epitaxial crystallites and growth hillocks was suppressed by the application of the oxygen-adding growth condition. Nitrogen was incorporated uniformly into the crystals, with a concentration variation of less than 10%. About 70% of the total nitrogen was substitutional nitrogen in a neutral charge state Ns0. Hydrogen was incorporated at approximately the same concentration as nitrogen. Both NV and NVH centers were predominantly negatively charged defect structures, i.e., NVâ and NHVâ centers. The concentrations of NHVâ centers were less than 5% of the total nitrogen concentration. Nitrogen concentration in diamond crystals was controlled by changing the N/C gas ratio over a wide doping range from 10 ppb to 10 ppm. Nitrogen incorporation efficiency was found to be (1.5 ± 0.5) Ă 10â4 in this study.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2015 - High-quality and high-purity homoepitaxial diamond (100) film growth under high oxygen concentration condition [Crossref]