Exploring High-Spin Color Centers in Wide Band Gap Semiconductors SiC - A Comprehensive Magnetic Resonance Investigation (EPR and ENDOR Analysis)

At a Glance

Metadata	Details
Publication Date	2024-06-26
Journal	Molecules
Authors	Лариса Латыпова, Fadis F. Murzakhanov, G. V. Mamin, Margarita A. Sadovnikova, H. J. von Bardeleben
Institutions	Sorbonne Université, Institute of Structure of Matter
Citations	3
Analysis	Full AI Review Included

Technical Analysis and Documentation: High-Spin Color Centers for Quantum Technologies

6CCVD Material Science Division Reference: Latypova et al., Exploring High-Spin Color Centers in Wide Band Gap Semiconductors SiC: A Comprehensive Magnetic Resonance Investigation (EPR and ENDOR Analysis). Molecules 2024, 29, 3033.

Executive Summary

This research validates the potential of nitrogen-vacancy (NV) centers in Silicon Carbide (SiC) polytypes (4H and 6H) as robust platforms for quantum computing and sensing applications, utilizing high-frequency magnetic resonance techniques.

Qubit Validation: NV centers in SiC were confirmed as robust electron qubits, meeting criteria for spin manipulation through the observation of Rabi oscillations.
Coherence Achievement: Achieved long phase coherence times (T₂ up to 60 µs at 150 K, and 25.3 µs at 275 K), demonstrating suitability for near-room temperature quantum technologies.
Precise Characterization: W-band (94 GHz) photoinduced EPR and ENDOR spectroscopy precisely determined the spin Hamiltonian parameters, including Zero-Field Splitting (D ≈ 1.2-1.3 GHz) and hyperfine/quadrupole interactions (A ≈ 1.1 MHz, C_q ≈ 2.45 MHz).
Multi-Qubit Potential: The presence of structurally nonequivalent NV centers in 6H-SiC allows for the selective excitation and readout of three independent qubits, crucial for quantum registers.
Spin-Photon Interface: The study established optimal optical excitation wavelengths (532 nm for 4H-SiC, 980 nm for 6H-SiC) necessary for optical initialization of the electron spin, enabling spin-photon interfaces.
Advanced Manipulation: Demonstrated the use of multipulse sequences (Hahn, CPMG) and resonant effects (MW/RF) on spin centers, essential for implementing quantum computing algorithms and CNOT gates.

Technical Specifications

The following hard data points were extracted from the EPR/ENDOR analysis of NV centers in 4H-SiC and 6H-SiC crystals:

Parameter	Value	Unit	Context
Zero-Field Splitting (D)	1.2 - 1.3	GHz	General range for NV centers in SiC
Axial ZFS Splitting (2D)	2330, 2548	MHz	Measured for 4H-SiC basal centers
Phase Coherence Time (T₂)	60	µs	Maximum T₂ observed (6H-SiC, T=150 K)
Room Temp T₂	25.3	µs	NV_kk centers in 4H-SiC (T=275 K)
Spin-Lattice Time (T₁)	1.42 - 1.43	ms	NV_kh/NV_hk in 4H-SiC (T=150 K)
Hyperfine Interaction (A_zz)	≈ 1.1	MHz	¹⁴N magnetic nuclei (I=1)
Quadrupole Interaction (C_q)	≈ 2.45	MHz	Axial symmetry
Isotropic Contribution (a)	-0.87 to -1.185	MHz	Basal NV centers
Anisotropic Contribution (b)	4 to 14	kHz	Basal NV centers
Optimal Excitation ($\lambda$)	532	nm	4H-SiC NV centers (Visible/Green)
Optimal Excitation ($\lambda$)	980	nm	6H-SiC NV centers (Near-IR)
EPR Operating Frequency	93.986	GHz	W-band spectroscopy

Key Methodologies

The experiments relied on precise material engineering and advanced pulsed magnetic resonance techniques:

Material Selection and Doping: Used commercial N-doped 4H-SiC (2 x 10¹⁷ cm^-3) and isotopically enriched 6H-²⁸SiC (99% ²⁸Si purity, N concentration ≈ 10¹⁷ cm^-3).
Defect Creation (Irradiation):
- 4H-SiC was irradiated with 12 MeV protons (fluence: 1 x 10¹⁶ cm^-2).
- 6H-SiC was irradiated with 2 MeV electrons (dose: 4 x 10¹⁸ cm^-2).
Defect Stabilization (Annealing): Both samples were annealed at T = 900 °C in an argon atmosphere to form stable negatively charged nitrogen-vacancy (V_SiN_C) complexes.
Spectroscopy Setup: Experiments were conducted using a Bruker Elexsys E680 spectrometer operating at 94 GHz (W-band) for high-resolution EPR/ENDOR.
Pulsed EPR Sequences: Dynamic parameters (T₁, T₂) were measured using standard pulse sequences:
- T₂: Hahn echo ($\pi/2 - \tau - \pi - \tau - ESE$) and Carr-Purcell-Meiboom-Gill (CPMG).
- T₁: Inversion-recovery ($\pi - T + dT - \pi/2 - \tau - \pi - \tau - ESE$).
- Rabi Oscillations: Three-pulse sequence used to confirm spin manipulation capability.
ENDOR Measurement: Electron-nuclear double resonance (ENDOR) spectra were obtained using the Mims pulse sequence, enabling indirect registration of NMR transitions to determine hyperfine and quadrupole constants.
Optical Pumping: Photoexcitation was achieved using solid-state lasers (532 nm to 1064 nm) integrated via an optical fiber into the sample holder, allowing simultaneous optical and MW/RF manipulation.

6CCVD Solutions & Capabilities

The research highlights the critical role of material purity, precise defect engineering, and advanced surface preparation in realizing quantum registers. While this study focused on SiC, 6CCVD specializes in MPCVD Diamond, the superior material platform for achieving the highest coherence times and integration capabilities required to advance this research.

Applicable Materials: The Diamond Advantage

Research Requirement (SiC)	6CCVD Diamond Solution (SCD/PCD)	Technical Advantage
Matrix for High-Spin Color Centers	Optical Grade Single Crystal Diamond (SCD)	Diamond NV centers (NV^-) offer T₂ coherence times in the millisecond range, vastly exceeding the 60 µs reported for SiC, crucial for robust quantum registers.
Isotopic Purity (²⁸Si)	Isotopically Purified ¹²C SCD	6CCVD supplies SCD with >99.999% ¹²C purity, minimizing nuclear spin noise (I=0) and maximizing T₂ coherence time, essential for multi-qubit registers.
Doping/Defect Engineering	Controlled Nitrogen Doping (SCD)	We offer precise control over nitrogen incorporation during growth, optimizing the precursor concentration necessary for high-yield NV center creation.
Integrated Qubit Structures	Boron-Doped Diamond (BDD)	For applications requiring integrated electrodes or high conductivity, 6CCVD provides BDD films, compatible with the electrical control methods necessary for quantum algorithms.

Customization Potential

The SiC samples used were small, custom-cut pieces (e.g., 0.8 mm x 0.4 mm x 0.2 mm). 6CCVD excels at providing materials tailored for complex experimental setups:

Custom Dimensions: We provide SCD and PCD plates/wafers in custom sizes, up to 125mm in diameter (PCD), and thicknesses ranging from 0.1 µm to 500 µm, ensuring compatibility with high-frequency W-band cavities (94 GHz).
Ultra-Smooth Polishing: The establishment of spin-photon interfaces requires high-quality optical surfaces. 6CCVD guarantees ultra-low surface roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ideal for integrating optical waveguides and resonators.
Integrated Metalization: To implement the complex MW/RF pulse sequences (Rabi, CPMG) and CNOT gates discussed in the paper, on-chip microwave delivery structures are necessary. 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu) for fabricating coplanar waveguides directly onto the diamond surface.

Engineering Support

The successful replication and extension of this research into diamond requires expertise in defect creation (irradiation and annealing) and material selection.

6CCVD’s in-house PhD team provides comprehensive engineering support for projects focused on NV Center Quantum Registers and Spin-Photon Interfaces. We assist researchers in optimizing:

Material Selection: Choosing the optimal SCD grade (e.g., high-purity ¹²C) to maximize T₂ coherence.
Defect Protocol: Consulting on post-growth processing, including irradiation parameters (fluence, energy) and annealing recipes (temperature, atmosphere) to maximize the yield and charge state stability of NV centers.
Device Integration: Advising on surface preparation and metalization schemes for integrated MW/RF control structures.

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

View Original Abstract

High-spin defects (color centers) in wide-gap semiconductors are considered as a basis for the implementation of quantum technologies due to the unique combination of their spin, optical, charge, and coherent properties. A silicon carbide (SiC) crystal can act as a matrix for a wide variety of optically active vacancy-type defects, which manifest themselves as single-photon sources or spin qubits. Among the defects, the nitrogen-vacancy centers (NV) are of particular importance. This paper is devoted to the application of the photoinduced electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) techniques at a high-frequency range (94 GHz) to obtain unique information about the nature and properties of NV defects in SiC crystal of the hexagonal 4H and 6H polytypes. Selective excitation by microwave and radio frequency pulses makes it possible to determine the microscopic structure of the color center, the zero-field splitting constant (D = 1.2-1.3 GHz), the phase coherence time (T2), and the values of hyperfine (≈1.1 MHz) and quadrupole (Cq ≈ 2.45 MHz) interactions and to define the isotropic (a = −1.2 MHz) and anisotropic (b = 10-20 kHz) contributions of the electron-nuclear interaction. The obtained data are essential for the implementation of the NV defects in SiC as quantum registers, enabling the optical initialization of the electron spin to establish spin-photon interfaces. Moreover, the combination of optical, microwave, and radio frequency resonant effects on spin centers within a SiC crystal shows the potential for employing pulse EPR and ENDOR sequences to implement protocols for quantum computing algorithms and gates.

Tech Support

Original Source

DOI: https://doi.org/10.3390/molecules29133033

References

2010 - Quantum Computers [Crossref]
2020 - Quantum Computers as Universal Quantum Simulators: State-of-the-Art and Perspectives [Crossref]
2008 - The Quantum Limit to Moore’s Law [Crossref]
2021 - Materials Challenges and Opportunities for Quantum Computing Hardware [Crossref]
2018 - Opportunities and Challenges for Quantum-Assisted Machine Learning in near-Term Quantum Computers [Crossref]
2019 - Quantum Error Correction: An Introductory Guide [Crossref]