Ultrafast room-temperature valley manipulation in silicon and diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-04-14 |
| Journal | Nature Physics |
| Authors | Adam Gindl, Martin Ämel, F. TrojĂĄnek, P. MalĂœ, Martin KozĂĄk |
| Institutions | Charles University |
| Analysis | Full AI Review Included |
Ultrafast Room-Temperature Valley Manipulation in Silicon and Diamond
Section titled âUltrafast Room-Temperature Valley Manipulation in Silicon and Diamondâ(Analysis of Nature Physics Article, Volume 21, June 2025, pp 947-952)
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a breakthrough in room-temperature valleytronics, utilizing MPCVD diamond to achieve ultrafast control over electron populations. This capability is essential for developing next-generation terahertz (THz) frequency devices.
- Ultrafast Valley Control: Achieved subpicosecond generation and read-out of valley-polarized electron populations in bulk diamond and silicon at room temperature (295 K).
- High Polarization Degree: Generated a significant degree of valley polarization (V â 0.33) in high-purity CVD diamond using non-resonant optical pumping.
- Femtosecond Methodology: The technique relies on linearly polarized infrared femtosecond pulses (40 fs duration) to induce unidirectional intervalley scattering.
- Room-Temperature Operation: Confirms the feasibility of valleytronic devices operating at room temperature, overcoming the need for cryogenic cooling previously required for long valley relaxation times.
- Fast Relaxation Time: Measured valley polarization relaxation time (Trel) in diamond was 9.7 ps at room temperature, enabling THz operational frequencies.
- Switching Capability: Demonstrated subpicosecond switching of the valley polarization direction using orthogonally polarized pump pulse pairs.
- Material Requirement: Success hinges on the use of high-purity, low-defect Single Crystal Diamond (SCD) material, aligning perfectly with 6CCVDâs core product line.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and Monte Carlo simulations, focusing on the diamond material parameters and experimental conditions.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Type | Single Crystal Diamond (CVD) | N/A | High-purity, [001] orientation |
| Sample Thickness (d) | 500 | ”m | Polished on both sides |
| Nitrogen Impurity | <5 | ppb | Specified by manufacturer |
| Boron Impurity | <1 | ppb | Specified by manufacturer |
| Longitudinal Effective Mass (ml) | 1.56 | mo | Diamond conduction band |
| Transverse Effective Mass (mt) | 0.28 | mo | Diamond conduction band |
| Pump Pulse Duration (Tp) | 40 | fs | Full-width at half-maximum |
| Pump Photon Energy | 0.62 | eV | Central wavelength 2,000 nm |
| Peak Electric Field (Fo) | 1.3 | V nm-1 | Diamond experiment |
| Pre-Excited Electron Density (N) | 6.4 x 1016 | cm-3 | Room temperature experiment |
| Max Valley Polarization (V) | â 0.33 | rel.u. | Achieved in diamond |
| Valley Polarization Relaxation Time (Trel) | 9.7 | ps | Diamond, Room Temperature (295 K) |
| Switching Time Scale | Subpicosecond | N/A | Demonstrated using orthogonal pump pulses |
Key Methodologies
Section titled âKey MethodologiesâThe experimental and theoretical approach utilized a sophisticated pump-probe setup combined with Boltzmann transport modeling to achieve and characterize ultrafast valley polarization.
- Carrier Generation: Electrons and holes were excited using a pre-excitation pulse (3.6 eV photon energy for diamond) to ensure an initial isotropic distribution across the six degenerate conduction band valleys.
- Thermalization Delay: A waiting time of 100 ps was introduced between the pre-excitation and the pump pulse to allow the electronic system to relax to the lattice temperature.
- Valley Polarization Generation: A linearly polarized infrared femtosecond pump pulse (40 fs, 0.62 eV) was applied along the [100] or [010] crystallographic direction. The oscillating electric field anisotropically accelerated electrons, driving unidirectional intervalley scattering based on effective mass anisotropy.
- Detection via Anisotropy: Valley polarization was detected by measuring the polarization anisotropy (Îα) of free-carrier absorption using a linearly polarized probe pulse (rotated 45°).
- Ultrafast Switching: The direction of valley polarization was switched on a subpicosecond timescale (1.4 ps delay) using a pair of orthogonally polarized pump pulses generated via a beta-barium borate crystal.
- Theoretical Validation: The dynamics were modeled by numerically solving the Boltzmann transport equation using a Monte Carlo approach, incorporating anisotropic effective mass tensors and energy-dependent intervalley electron-phonon scattering mechanisms.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms Single Crystal Diamond (SCD) as a critical platform for next-generation valleytronic and THz devices. 6CCVD is uniquely positioned to supply the high-specification materials required to replicate and advance this work.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the high-performance results achieved in this study, researchers require diamond material with extremely low defect density and precise orientation control.
- Optical Grade Single Crystal Diamond (SCD): This is the essential material. 6CCVD guarantees SCD with ultra-low nitrogen (<1 ppb) and boron (<1 ppb) concentrations, minimizing defect-assisted scattering that limits valley relaxation time (Trel).
- Boron-Doped Diamond (BDD): For future integration requiring electrical contacts or p-type layers, 6CCVD offers custom BDD layers, enabling the development of fully integrated valleytronic transistors or Hall effect measurement structures.
Customization Potential
Section titled âCustomization PotentialâThe success of this experiment relied on specific material geometry and quality. 6CCVDâs custom capabilities ensure seamless integration into advanced research setups.
| Research Requirement | 6CCVD Capability | Engineering Specification |
|---|---|---|
| Crystallographic Orientation | Custom Orientation Control | SCD wafers available with precise [001] surface normal orientation, critical for aligning the valleys with the pump polarization direction. |
| Thickness Matching | SCD Thickness Control | We provide SCD plates matching the required 500 ”m thickness, with custom options ranging from 0.1 ”m to 500 ”m. |
| Surface Finish | Ultra-Precision Polishing | SCD wafers polished to Ra < 1 nm on both sides, ensuring minimal optical scattering losses for pump-probe spectroscopy. |
| Future Device Integration | Custom Metalization Services | For subsequent electrical read-out experiments (e.g., time-of-flight measurements), 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu contacts. |
| Large-Area Scalability | Polycrystalline Diamond (PCD) | For scaling up THz components, 6CCVD offers PCD wafers up to 125 mm diameter, polished to Ra < 5 nm. |
Engineering Support
Section titled âEngineering SupportâThe development of room-temperature valleytronic devices operating at THz frequencies is a complex, multidisciplinary challenge. 6CCVDâs in-house PhD team specializes in the material science of MPCVD diamond and can assist researchers with:
- Material Selection: Optimizing SCD purity and orientation for specific intervalley scattering regimes.
- Custom Recipe Development: Tailoring CVD growth parameters to achieve specific defect profiles or doping levels necessary for extending this ultrafast valley manipulation research.
- Integration Consultation: Advising on optimal metalization schemes and polishing specifications for integrated THz valleytronic devices.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Some semiconductors have more than one degenerate minimum of the conduction band in their band structure. These minimaâknown as valleysâcan be used for storing and processing information, if it is possible to generate a difference in their electron populations. However, to compete with conventional electronics, it is necessary to develop universal and fast methods for controlling and reading the valley quantum number of the electrons. Even though selective optical manipulation of electron populations in inequivalent valleys has been demonstrated in two-dimensional crystals with broken time-reversal symmetry, such control is highly desired in many technologically important semiconductor materials, including silicon and diamond. We demonstrate an ultrafast technique for the generation and read-out of a valley-polarized population of electrons in bulk semiconductors on subpicosecond timescales. The principle is based on the unidirectional intervalley scattering of electrons accelerated by an oscillating electric field of linearly polarized infrared femtosecond pulses. Our results are an advance in the development of potential room-temperature valleytronic devices operating at terahertz frequencies and compatible with contemporary silicon-based technology.