Silicon carbide detectors for sub-GeV dark matter
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-04-06 |
| Journal | Physical review. D/Physical review. D. |
| Authors | Sinéad M. Griffin, Yonit Hochberg, Katherine Inzani, Noah Kurinsky, Tongyan Lin |
| Institutions | Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory |
| Citations | 86 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Novel Target Material: Silicon Carbide (SiC) is proposed as a highly versatile and scalable target material for the direct detection of sub-GeV Dark Matter (DM), addressing limitations found in Silicon (Si) and Diamond (C).
- Tunable Properties: SiC exhibits polymorphism (e.g., 3C, 2H, 4H, 6H), allowing for material-by-design optimization. Its polar nature provides unique sensitivity to Dark Photon interactions, unlike non-polar diamond.
- Broad DM Reach: Projected sensitivity covers DM scattering (electron, nuclear, and phonon excitations) down to 10 keV DM mass and DM absorption processes down to 10 meV DM mass.
- Ultra-Low Resolution: Reference designs for cryogenic phonon calorimeters project achievable energy resolutions as low as 0.5 meV, enabling the detection of single optical phonon excitations (100-120 meV).
- Directional Detection: Hexagonal polytypes (H-SiC), particularly 2H, exhibit strong crystal anisotropy, leading to a significant daily modulation in the DM signal rate, which is crucial for directional detection and background rejection.
- Scalability and Hardness: SiC is commercially available in large wafers (unlike diamond), ensuring cost-effective scaling to kg-year exposures, and possesses superior radiation hardness and a higher band gap (up to 3.33 eV) compared to Si.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Band Gap (Egap) | 2.39 to 3.33 | eV | Varies by polytype (3C is lowest, 2H is highest) |
| Pair Creation Energy (Eeh) | 5.7 to 10.5 | eV | Energy cost to produce one electron-hole pair |
| Sound Speed (cs) | 11,900 to 16,300 | m/s | Calculated values across polytypes |
| Highest Optical Phonon Energy (ħÏLO) | 119.5 to 120.7 | meV | Consistent across all polytypes |
| Dielectric Constant (Δ0,â„) | 9.67 to 10.40 | - | Relative permittivity perpendicular to c-axis |
| Charge Resolution (Ïq) | 0.25 to 1.4 | e-h+ pairs | Charge readout designs (segmented vs. single cell) |
| Phonon Resolution (Ïph) | 0.5 to 200 | meV | Reference designs (D to A) for calorimetric readout |
| Detector Mass (Design A) | 145 | g | 6H or 4H polytype, 1 cm thick |
| Maximum Drift Length (4H-SiC) | 2.4 | cm | Measured at 8 kV/cm field strength |
| Phonon Lifetime (3C, 2 K) | ~30 | ms | Calculated average for acoustic phonons (0-2 THz) |
| Reference NEP (Design C/D) | 10-20 | W/âHz | Benchmark noise power for quantum sensors |
| Bias Voltage (Charge Readout) | 4 to 500 | kV or V | Required for full charge collection (8 kV/cm field) |
Key Methodologies
Section titled âKey MethodologiesâThe research relies on state-of-the-art theoretical modeling and simulation, applying established detector performance models to calculated material properties:
- First-Principles Calculations (DFT): Full geometry optimizations were performed using Density Functional Theory (DFT) via the Vienna Ab initio Simulation Package (VASP) and projector augmented wave (PAW) pseudopotentials.
- Electronic Structure Determination: Band structures and wavefunctions were calculated using the Heyd-Scuseria-Ernzerhof (HSE06) screened hybrid functional to ensure excellent agreement with experimental band gaps (Table I).
- Phonon Property Calculation: Force constants, phonon dispersion spectra, and Born effective charges were calculated using the finite displacement method (VASP and PHONOPY).
- Phonon Lifetime Modeling: Phonon-phonon interactions and lifetimes were calculated using the PHONO3PY code. Acoustic lifetimes were averaged in the 0-2 THz frequency range, yielding lifetimes up to ~30 ms for 3C SiC at 2 K.
- Detector Performance Modeling: Expected charge (Ïq) and phonon (Ïph) resolutions were determined using a technology-agnostic model based on material properties (sound speed, Egap) and benchmark noise equivalent power (NEP) targets for cryogenic sensors (e.g., TES, SNS Junctions).
- DM Interaction Rate Calculation: DM scattering and absorption rates were computed using the Standard Halo Model velocity distribution, incorporating material structure factors derived from the calculated electronic and phonon spectra for each polytype.
- Directional Sensitivity Modeling: Daily modulation rates were calculated by accounting for the time-dependent direction of the Earthâs velocity relative to the anisotropic crystal axes of the hexagonal polytypes.
Commercial Applications
Section titled âCommercial ApplicationsâSiCâs unique combination of wide band gap, high thermal conductivity, radiation hardness, and commercial scalability makes it critical for several high-tech sectors, complementing its proposed use in DM detection:
- Radiation and Particle Detection: SiC is a proven replacement for Si in high-radiation environments (e.g., nuclear reactors, space) due to its superior radiation hardness. Applications include microstrip detectors, high-energy resolution detectors, and beam monitors in particle accelerators.
- High-Temperature/High-Power Electronics: The wide band gap allows SiC devices to operate at higher temperatures and voltages than Si, making them essential for power electronics, inverters, and high-frequency applications.
- UV Sensing Technology: SiCâs high band gap (up to 3.33 eV) provides intrinsic UV sensitivity and low leakage current, making it ideal for UV photodiodes and sensors.
- Cryogenic Quantum Sensing: SiC serves as an excellent substrate for cryogenic calorimeters (microcalorimeters) due to its high sound speed and long intrinsic phonon lifetime, supporting the development of ultra-low noise sensors (e.g., TES, KIDs) for fundamental physics and quantum computing.
- Materials-by-Design (Polymorphism): The ability to synthesize multiple stable polytypes (3C, 4H, 6H) allows for targeted material selection based on specific electronic or directional requirements, enabling specialized sensor development.
View Original Abstract
We propose the use of silicon carbide (SiC) for direct detection of sub-GeV dark matter. SiC has properties similar to both silicon and diamond but has two key advantages: (i) it is a polar semiconductor which allows sensitivity to a broader range of dark matter candidates; and (ii) it exists in many stable polymorphs with varying physical properties and hence has tunable sensitivity to various dark matter models. We show that SiC is an excellent target to search for electron, nuclear and phonon excitations from scattering of dark matter down to 10 keV in mass, as well as for absorption processes of dark matter down to 10 meV in mass. Combined with its widespread use as an alternative to silicon in other detector technologies and its availability compared to diamond, our results demonstrate that SiC holds much promise as a novel dark matter detector.