Spin coherence as a function of depth for high-density ensembles of silicon vacancies in proton-irradiated 4H–SiC
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-07-18 |
| Journal | Solid State Communications |
| Authors | Peter Brereton, D. Puent, J. R. Vanhoy, E. R. Glaser, S.G. Carter |
| Institutions | United States Naval Research Laboratory, United States Naval Academy |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- Core Value Proposition: This research validates proton irradiation as a viable, scalable method for generating high-density ensembles of silicon vacancies (VSi) in 4H-SiC, crucial for solid-state quantum applications.
- Depth Dependence of Coherence: The spin coherence time (T2) of the VSi ensemble was measured as a function of implantation depth, correlating T2 directly with defect density.
- Coherence Time Results: T2 decreased significantly from a maximum of 11.5 µs near the irradiated surface (low density) to 3.4 µs at approximately 40 µm depth (high density).
- Decoherence Mechanism Identified: The strong correlation between decreasing T2 and increasing integrated photoluminescence (PL) intensity (defect density) confirms that dipole-dipole interactions between neighboring VSi are the dominant decoherence mechanism in these high-density ensembles.
- Material Advantage: SiC VSi defects offer significant material benefits over canonical nitrogen vacancies (NV) in diamond, including robust industrial microfabrication capacity and emission in telecom-compatible wavelengths.
- Engineering Implications: The ability to engineer defect density and coherence time through precise proton implantation depth is critical for fabricating scalable SiC quantum devices and achieving superradiant coupling.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | High purity semi-insulating 4H-SiC | N/A | Commercial CREE substrate |
| Defect Studied | Silicon Vacancy (VSi) V2 transition | N/A | S = 3/2 ground state |
| Irradiation Particle | Proton (H+) | N/A | Used to generate defects |
| Irradiation Energy | 2 | MeV | Tandem linear accelerator source |
| Proton Fluence | 3.5 x 1015 | proton/cm2 | Total dose applied |
| Projected Proton Range | 32 | µm | Calculated stopping depth into bulk crystal |
| Excitation Wavelength | 850 | nm | Below-gap excitation for PL |
| Static Magnetic Field (Bstatic) | 68.5 | mT | Applied parallel to the c-axis |
| VSi Ground State Splitting (2D) | 70 | MHz | Zero external magnetic field |
| ODMR Transition Frequency | 2022 | MHz | Used for Rabi/Hahn echo measurements |
| Maximum Coherence Time (T2) | 11.5 | µs | Measured near the irradiated surface (low density) |
| Minimum Coherence Time (T2) | 3.4 | µs | Measured near 40 µm depth (high density) |
| Low Temperature PL Peaks | 1438, 1353 | meV | V1 and V2 zero-phonon lines (ZPL) |
Key Methodologies
Section titled “Key Methodologies”The experiment utilized proton irradiation to generate defects and optically detected magnetic resonance (ODMR) combined with pulsed techniques to measure spin coherence as a function of depth.
-
Sample Preparation (Proton Irradiation):
- High-purity semi-insulating 4H-SiC substrates were flood irradiated in air.
- A 2 MeV proton beam was directed parallel to the c-axis.
- A high fluence of 3.5 x 1015 proton/cm2 was used, resulting in a calculated projected proton range of 32 µm.
- No annealing step was performed, meaning emission was measured from natural and unannealed radiation damage defects.
-
Optical Setup and Scanning:
- Defect photoluminescence (PL) was excited using 850 nm light from a Ti:sapphire laser focused through a microscope objective (0.65 NA, 50x).
- The excitation and collection were arranged confocally along the cleaved edge of the sample.
- A stepper motor stage was used to scan the measurement volume from the irradiated face into the bulk, allowing depth-dependent measurements.
-
Microwave Control and ODMR:
- Microwave excitation was delivered via a 50 µm diameter gold wire loop shorted between the center electrode and the outer conductor of a coaxial cable.
- A static magnetic field (68.5 mT) was applied parallel to the c-axis.
- Continuous wave ODMR was used to identify the spin transitions (1883 MHz and 2022 MHz).
-
Pulsed Coherence Measurement (Hahn Echo):
- To measure the single defect coherence time (T2), the Hahn echo sequence was employed to remove inhomogeneous dephasing (T2*).
- Sequence: Optical pump pulse (spin polarization) → π/2 microwave pulse (superposition state) → fixed delay T → π pulse (spin reversal) → variable delay t → final π/2 pulse → final off-resonant optical pulse (readout).
- The damping of the coherent echo signal was fit to determine T2 at various depths within the sample.
Commercial Applications
Section titled “Commercial Applications”The successful engineering of high-density, coherent spin ensembles in SiC directly supports the development of next-generation quantum technologies.
- Solid-State Quantum Computing: SiC VSi centers serve as robust, optically addressable spin qubits, offering a scalable platform compatible with existing semiconductor microfabrication infrastructure.
- Quantum Sensing and Metrology: The spin coherence properties enable high-sensitivity magnetic field sensing (magnetometry) and nanoscale nuclear magnetic imaging, potentially surpassing current diamond NV center limitations in certain environments.
- Superradiant Devices: Achieving high defect densities (approaching 1016 spins/mm3) is necessary for demonstrating strong radiative coupling, leading to:
- Chip-Scale Ultra-Stable Lasers: Utilizing superradiant emission for highly stable, compact light sources.
- High-Sensitivity Detectors: Quantum-enhanced detectors leveraging collective spin effects.
- Quantum Communication: VSi defects emit in the near-infrared (V2 transition at 1353 meV), which corresponds to telecom-compatible wavelength bands, enabling long-distance quantum network links.
- Engineered Defect Manufacturing: The use of proton irradiation provides a precise, depth-controlled method for generating defect layers, allowing for the integration of quantum functionality directly into SiC electronic or photonic devices.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2003 - Long coherence times at 300 k for nitrogen-vacancy center spins in diamond grown by chemical vapor deposition [Crossref]
- 2004 - Observation of coherent oscillations in a single electron spin [Crossref]
- 2009 - Ultralong spin coherence time in isotopically engineered diamond [Crossref]
- 2000 - Stable solid-state source of single photons [Crossref]
- 2012 - A robust scanning diamond sensor for nanoscale imaging with single nitrogen-vacancy centres [Crossref]
- 2013 - Optical magnetic imaging of living cells [Crossref]
- 2013 - Nanoscale magnetic imaging of a single electron spin under ambient conditions [Crossref]
- 2008 - Nanoscale magnetic sensing with an individual electronic spin in diamond [Crossref]
- 2014 - Subnanometre resolution in three-dimensional magnetic resonance imaging of individual dark spins [Crossref]
- 2010 - Quantum computing with defects [Crossref]