Characterization of oxygen defects in diamond by means of density functional theory calculations

At a Glance

Metadata	Details
Publication Date	2016-09-09
Journal	Physical review. B./Physical review. B
Authors	Gergő Thiering, Ádám Gali
Institutions	Hungarian Academy of Sciences, Budapest University of Technology and Economics
Citations	39
Analysis	Full AI Review Included

6CCVD Technical Documentation: Oxygen Point Defects in Diamond

Analysis of DFT Characterization for Quantum Applications

This documentation analyzes the theoretical characterization of oxygen point defects in MPCVD diamond, detailing key findings related to electronic structure, magneto-optical properties, and their potential use as solid-state qubits or sensors. The analysis highlights the specific material requirements necessary to replicate and extend this foundational research using 6CCVD’s advanced Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates.

Executive Summary

Core Research Focus: Systematic DFT (Density Functional Theory) characterization of interstitial (O_BC), substitutional (O_S), oxygen-vacancy (OV), and hydrogen complexes (OVH, O_SH) in diamond, validating previously observed Electron Spin Resonance (ESR) and Photoluminescence (PL) centers.
Defect Identification Supported: The study strongly supports the identification of the WAR5 ESR center as the neutral oxygen-vacancy defect (OV(0)) and the OVH ESR center as the neutral oxygen-vacancy-hydrogen complex (OVH(0)).
KUL12 Center Identified: The positively charged substitutional oxygen defect (O_S(+)) is robustly identified as the KUL12 ESR center, which is highly relevant for researchers utilizing ion implantation (specifically $^{17}$O) techniques.
Qubit Suitability Assessment: The critical finding is that OV(0), despite being isovalent to the NV(-) center, exhibits a predicted very fast non-radiative decay ($\sim$THz tunneling rate) from its excited state, rendering it unsuitable as an NV-like solid-state qubit due to expected weak or no luminescence.
Methodological Precision: Highly accurate hybrid DFT calculations (HSE06) using large 512-atom supercells and constrained DFT methods were utilized to predict ZPLs, hyperfine tensors, and the dynamic effects of Jahn-Teller distortion (motional averaging).
Material Requirement: Replicating these defects requires extremely high-purity, low-nitrogen CVD diamond (SCD), often requiring custom control over Fermi level positioning via n-type (P) or p-type (B) doping to stabilize specific charge states.

Technical Specifications

The following hard data points were extracted from the theoretical calculations and comparisons to experimental data:

Parameter	Value	Unit	Context
Supercell Size	512	atoms	DFT calculation scale for defects
DFT Functional (Equilibrium)	PBE	N/A	Calculated lattice constant: 3.565 Å
DFT Functional (Qubit/Optics)	HSE06	N/A	Calculated lattice constant: 3.545 Å
Plane Wave Energy Cutoff	370 / 600	eV	Standard / Hyperfine calculations, respectively
Calculated Raman Mode	1326	cm^-1	Validation of PBE functional against experiment (1332 cm^-1)
OV(0) Calculated ZPL	2.34	eV	Lowest spin-conserving optical transition
Associated Experimental PL	2.28 (543.2)	eV (nm)	Observed 543.2 nm PL center in CVD diamond
OV(0) D-Tensor (Calc)	2989	MHz	Zero-Field Splitting (ZFS) due to spin-spin interaction (S=1)
WAR5 D-Tensor (Exp)	2888(2)	MHz	Experimental ZFS value supporting OV(0) identification
O_BC Diffusion Barrier	3.13	eV	Indicates interstitial oxygen is highly immobile in the lattice
OVH(0) Tunneling Rate ($\Gamma_E$)	25.5	THz	Extremely high rate confirms motional averaging (high symmetry ESR)
O_S(+) Tunneling Rate ($\Gamma_T$)	0.3	GHz	Low rate compared to Q-band ($\approx$34 GHz) measurements, confirming static symmetry detection
OV(+) ZPL (Calc)	2.45	eV	SCD material candidate for 543.2 nm PL center

Key Methodologies

The study relied on sophisticated computational physics techniques to accurately model highly correlated electron systems in the diamond lattice.

DFT Supercell Setup:
- Used a large cubic 512-atom supercell for highly localized defect studies, ensuring minimal interaction between periodic images (Brillouin zone sampling only at the $\Gamma$ point).
- Employed the standard Projector Augmented-Wave (PAW) method.
Functional Selection:
- Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation used for geometry optimization and vibrational properties (phonons/PES barriers).
- HSE06 screened hybrid functional used for accurate calculations of charge transition levels, ZPLs, and magneto-optical properties, providing good quantitative agreement for diamond defects.
Calculation of Transition Energies:
- Formation Energy: Calculated as a function of the Fermi level (E(q) / E_F), referenced against the valence band edge (E_V).
- Optical Transitions (ZPL): Determined using the ASCF method (constrained DFT) to calculate the energy difference between relaxed ground and excited states.
Magneto-Optical Characterization:
- Calculated D-tensors (Zero-Field Splitting, ZFS) for S=1 defects (OV(0), O_S(0) triplet state).
- Calculated Hyperfine Tensors (A constants) for electron spin coupling to proximate nuclei ($^{13}$C, $^{17}$O, $^1$H), including core spin polarization effects.
Jahn-Teller and Dynamics Modeling:
- Modeled motional averaging effects in dynamic Jahn-Teller systems (like OVH(0)) using a full potential energy surface (PES) approach and calculating the tunneling rate ($\Gamma$) between equivalent distorted configurations.

6CCVD Solutions & Capabilities

This research confirms that controlled synthesis and material engineering are paramount for investigating complex oxygen and hydrogen defects. 6CCVD is uniquely positioned to supply the advanced diamond materials and processing services required to replicate or advance these quantum defect studies.

Applicable Materials

To replicate the high-purity environment and controlled doping required for oxygen defect research, 6CCVD recommends the following specialized CVD diamond products:

Research Requirement	6CCVD Recommended Material	Material Properties
High-Purity Host (OV/O_S)	High Purity Optical Grade SCD	Lowest residual nitrogen (< 1 ppb N) ensures only intentionally introduced oxygen/vacancy defects dominate spectroscopy. Ideal for quantum coherence studies.
Positive Charge State Stabilization (O_S(+))	Custom Boron-Doped (BDD) SCD	P-type doping stabilizes positive charge states. Required for isolating the O_S(+) / KUL12 center (stabilized for E_F $\approx$ 0.32 - 2.19 eV).
Negative Charge State Stabilization (OV(-))	Custom Phosphorus-Doped PCD	N-type doping (e.g., P) is required to stabilize negative charge states, such as OV(-) and OVH(-), which are only marginally stable in highly doped material.
Ion Implantation Substrate	Custom Thickness SCD/PCD Plates	SCD plates (0.1µm - 500µm) or Substrates (up to 10mm) provide optimal targets for oxygen ion implantation ($^{16}$O or $^{17}$O).

Customization Potential

The experimental realization of these defects often necessitates precise substrate preparation and post-processing, capabilities fully supported by 6CCVD:

Custom Dimensions: We offer plates and wafers up to 125mm in diameter (PCD) and custom SCD dimensions, allowing engineers to standardize sample size for comparative spectroscopic measurements.
Precision Polishing: Defect creation (via implantation or etching) requires pristine surfaces. 6CCVD guarantees ultra-low roughness polishing:
- SCD: Surface roughness (Ra) less than 1 nm.
- Inch-size PCD: Surface roughness (Ra) less than 5 nm.
Metalization Services: While the paper focuses on intrinsic defect properties, integrating these centers into functional devices (e.g., microwave circuits for ESR/ODMR) requires customized electrical contacts. 6CCVD offers expert, in-house metalization using thin film deposition of: Au, Pt, Pd, Ti, W, and Cu.

Engineering Support

This study underscores the complexity of engineering specific charge states and defect complexes through controlled growth and processing.

6CCVD’s in-house team of PhD material scientists is available to assist researchers with material selection, doping level specification, and substrate preparation necessary for replicating or extending these oxygen-related point defect projects.
We provide consultation on the optimization of post-growth treatments (e.g., annealing steps, as discussed in the paper for stabilizing centers like KUL12 after 1500 °C annealing) based on desired final defect stability and charge state.

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

View Original Abstract

Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations within density functional theory, in order to characterize the electronic and magneto-optical properties of various oxygen-related defects. Beside the trivial single interstitial and substitutional oxygen defects we also consider their complexes with vacancies and hydrogen atoms. We find that oxygen defects are mostly electrically active and introduce highly correlated orbitals that pose a challenge for density functional theory modeling. Nevertheless, we are able to identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance spectrum. We demonstrate that first principles calculations can predict the motional averaging of the electron paramagnetic resonance spectrum of defects that are subject to Jahn-Teller distortion. We show that the high-spin neutral oxygen-vacancy defect exhibits very fast non-radiative decay from its optical excited state that might hinder to apply it as a qubit.