Incorporation of Large Impurity Atoms into the Diamond Crystal Lattice - EPR of Split-Vacancy Defects in Diamond

At a Glance

Metadata	Details
Publication Date	2017-07-31
Journal	Crystals
Authors	Vladimir A. Nadolinny, Andrey Komarovskikh, Yuri N. Palyanov
Institutions	Nikolaev Institute of Inorganic Chemistry, Novosibirsk State University
Citations	53
Analysis	Full AI Review Included

6CCVD Technical Documentation: Defect Engineering in CVD Diamond

Reference Paper: Incorporation of Large Impurity Atoms into the Diamond Crystal Lattice: EPR of Split-Vacancy Defects in Diamond (Review)

Executive Summary

This expert review confirms the viability of incorporating large atomic radius impurities (Ni, Co, Ti, P, Si, Ge) into the diamond crystal structure, a critical prerequisite for advanced quantum and semiconductor applications.

Defect Stabilization via Annealing: High-Pressure High-Temperature (HPHT) annealing (1800 K to 2600 K) is crucial for relaxing lattice strain caused by large substitutional atoms, leading directly to the formation of stable, complex split-vacancy defects.
Key Defect Structures: The research details the formation of transition metal split-vacancy centers (e.g., Nickel-Nitrogen complexes NE1-NE9) and Group IV vacancy centers (SiV⁰, GeV⁰), which possess favorable electronic and spin properties.
Quantum Relevance: Silicon-Vacancy (SiV⁻) and Germanium-Vacancy (GeV⁻) centers, identified as split-vacancy defects (S=1 or S=1/2), are highlighted as leading candidates for room-temperature single-photon sources and quantum memories.
Controlling Charge State: Nitrogen impurities act as critical electron donors or “getters,” driving defect aggregation via Coulomb interactions and influencing the final charge state and stability of the engineered centers (e.g., preventing n-type conductivity in P-doped systems).
Advanced Characterization: Spin-Hamiltonian parameters, including g-tensors, Hyperfine Structure (HFS) constants, and Zero-Field Splitting (ZFS), derived from Electron Paramagnetic Resonance (EPR) analysis, provide precise microscopic models for defect engineering.

Technical Specifications

The following parameters summarize the critical physical data and experimental conditions required for defect creation and characterization detailed in the review.

Parameter	Value	Unit	Context
HPHT Annealing Maximum	2700	K	Upper temperature limit for nitrogen aggregation studies.
Split-Vacancy Formation Temperature (Ni)	≥ 2100	K	Temperature threshold for NE1/NE5 appearance.
Split-Vacancy Formation Temperature (Ti/Ge)	≥ 2300	K	Temperature threshold for OK1 (Ti-V) and GeV⁰ formation.
Standard C-C Bond Length in Diamond	1.54	Å	Reference lattice parameter.
Ni-C / Ti-C Defect Bond Length	~2	Å	Indicates high internal strain at substitutional sites.
Neutral Silicon-Vacancy (SiV⁰) Spin State	S = 1	N/A	Characterized by the KUL1 spectrum.
Neutral Germanium-Vacancy (GeV⁰) Spin State	S = 1	N/A	Measured axial symmetry (g_\|\| = 2.0025).
SiV⁰ Zero-Field Splitting (D)	35.8	mT	Indicates energy separation of spin sublevels.
GeV⁰ Zero-Field Splitting (D) (Experimental)	80.3	mT	Higher D value attributed to high spin-orbit coupling of Ge.
Nitrogen Impurity Concentration (Type I)	~10²⁰	cm^-3	Maximum concentration detected by mass spectrometry.
N3 Photoluminescence (PL) Zero-Phonon Line	440.3	nm	Associated with Titanium-Nitrogen centers.
SiV⁻ Photoluminescence (PL) Zero-Phonon Line	737	nm	Negatively charged Silicon-Vacancy center.

Key Methodologies

The experimental procedures for synthesizing and transforming complex point defects rely heavily on precise control over material synthesis and post-processing thermal budgets.

HPHT Material Synthesis: Diamond crystals were grown using metal solvent-catalyst systems (e.g., Fe-Ni-C, Ni-C, Mg-Ge-C). Control over the chemical composition of the melt was necessary for initial incorporation of large impurity atoms (Ni, Co, Ti, P, Si, Ge) and isotopic markers (e.g., ⁶¹Ni, ¹³C, ⁷³Ge).
Substitutional Defect Formation: During growth at relatively lower temperatures (e.g., 1700 K), large impurity atoms initially occupied substitutional positions, leading to significant local lattice strain (e.g., W8 Ni defect, MA1 P defect).
High-Temperature Annealing Protocol: Samples were subjected to controlled HPHT annealing, often for several hours (3-18 h) across a wide range (1800 K to 2600 K). This thermal energy provided the activation required for structural relaxation and defect migration.
Split-Vacancy Transformation: Annealing caused the strained substitutional impurity atom to displace a nearest carbon neighbor, creating a mobile interstitial carbon atom (C_I) and forming the stable, lower-strain split-vacancy configuration (e.g., Ni split-vacancy unit).
Impurity Aggregation via Diffusion: Nitrogen atoms (often present as background or intentionally doped) diffused through the lattice at high temperatures, driven by Coulomb attraction towards the charged metal split-vacancy units, forming complex multi-atom defects (e.g., NE1, NP3).
Characterization: EPR spectroscopy was the primary technique used to determine the microscopic structure, symmetry (e.g., C_3v, C_2h), spin state (S), and orientation of the paramagnetic centers, often complemented by Photoluminescence (PL) to track optically active centers like SiV and GeV.

6CCVD Solutions & Capabilities

This research into engineered defects (Ni-N, SiV, GeV) demonstrates the crucial need for ultra-high purity, custom-doped, and precisely processed diamond substrates. 6CCVD is uniquely positioned to supply the foundational materials required to replicate and advance this cutting-edge quantum and semiconductor research.

Applicable Materials

To achieve the precise defect incorporation and transformation studied in this paper, researchers require material platforms with controlled purity and doping profiles. 6CCVD offers the following critical starting materials via MPCVD synthesis:

Optical Grade Single Crystal Diamond (SCD): Ideal for replicating SiV and GeV studies. Our SCD wafers offer exceptionally low intrinsic nitrogen concentration, ensuring that ion implantation or targeted doping (Si, Ge) results in highly localized and stable split-vacancy centers without interference from background nitrogen complexes.
Polycrystalline Diamond (PCD) Platforms: For large-scale synthesis or HPHT/CVD hybrid experiments where large area substrates are needed (up to 125mm). Our high-purity PCD offers excellent thermal management for high-temperature annealing protocols (up to 2700 K as noted in the paper).
Custom Boron-Doped Diamond (BDD): The paper highlights that p-type doping (Boron) is fundamental to controlling the charge state of defects (e.g., SiV⁻). 6CCVD can supply controlled Boron-Doped SCD or PCD films, necessary for achieving high yields of the negatively charged, optically active SiV⁻ and GeV⁻ centers.

Customization Potential

The success of defect engineering relies on precise material dimensions and post-synthesis processing, areas where 6CCVD provides unparalleled control:

Process Requirement from Paper	6CCVD Customization Solution	Benefit to Researcher
High-Purity (Low N) Substrates	Custom MPCVD growth recipes (low BDD, high-purity SCD).	Ensures precise control over defect precursor concentration.
High-Precision Polishing (SiV/GeV)	Ra < 1nm SCD Polishing.	Minimizes surface damage, crucial for maximizing PL signal coherence and integration into photonic devices.
Custom Metallization Layers	Internal capability for Au, Pt, Ti, W, Cu.	Essential for creating conductive contacts or masking layers for targeted ion implantation (used to introduce Si or Ge).
Non-Standard Dimensions	Plates/wafers up to 125mm (PCD); custom thickness SCD (0.1µm - 500µm).	Allows researchers to scale up defect creation or fabricate large-area sensing arrays.

Engineering Support

The creation of stable quantum emitters like SiV and GeV requires expertise bridging material science and quantum physics. 6CCVD’s in-house PhD team can assist with material selection for similar Quantum Emitter and Solid-State Sensor projects. We provide consultation on:

Precursor Doping: Selecting the optimal doping gas ratios for Si or Ge incorporation during MPCVD growth.
Strain Management: Providing low-strain, highly polished substrates necessary for maintaining the coherence time of group IV split-vacancy defects.
Thermal Budget Optimization: Advising on the material specifications best suited to survive the extreme temperatures (up to 2600 K) required for defect transformation and aggregation.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Diamond is a unique mineral widely used in diverse fields due to its remarkable properties. The development of synthesis technology made it possible to create diamond-based semiconductor devices. In addition, doped diamond can be used as single photon emitters in various luminescence applications. Different properties are the result of the presence of impurities or intrinsic defects in diamond. Thus, the investigation of the defect formation process is of particular interest. Although hydrogen, nitrogen, and boron have been known to form different point defects, the possibility for large impurity atoms to incorporate into the diamond crystal structure has been questioned for a long time. In the current paper, the paramagnetic nickel split-vacancy defect in diamond is described, and the further investigation of nickel-, cobalt-, titanium-, phosphorus-, silicon-, and germanium-related defects is discussed.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst7080237

References

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