High-throughput calculation screening for new silicon allotropes with monoclinic symmetry
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-05-31 |
| Journal | IUCrJ |
| Authors | Qingyang Fan, Jie Wu, Yingbo Zhao, Yanxing Song, Sining Yun |
| Institutions | Xidian University, Xiâan University of Architecture and Technology |
| Citations | 21 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Monoclinic Silicon Allotropes
Section titled âTechnical Documentation & Analysis: Monoclinic Silicon AllotropesâExecutive Summary
Section titled âExecutive SummaryâThis high-throughput computational study identifies 87 novel monoclinic silicon (Si) allotropes, offering potential materials for next-generation optoelectronic devices by addressing the inherent limitations of standard diamond Si (indirect band gap).
- Targeted Application: The research focuses on identifying Si allotropes suitable for photovoltaic and optoelectronic applications, specifically those exhibiting direct or quasi-direct band gaps.
- Electronic Properties: 13 new allotropes (14.94% of semiconductors) exhibit direct or quasi-direct band gaps, overcoming the primary limitation of standard diamond Si.
- Superior Carrier Transport: Five new allotropes demonstrate electron effective masses ($m_e$) significantly smaller than diamond Si, indicating potential for superior carrier mobility and transport performance.
- Enhanced Mechanical Benchmarks: Three new Si allotropes show bulk moduli greater than that of diamond Si (up to 99 GPa vs. 88 GPa), challenging diamond Siâs mechanical dominance.
- Optical Performance: All 74 semiconductor allotropes exhibit strong absorption capacity in the visible spectral region, confirming their promise for solar cell applications.
- 6CCVD Value Proposition: While these Si allotropes are promising, 6CCVD provides the ultimate benchmark materialâMPCVD Diamond (SCD/PCD)âwhich offers unparalleled thermal, mechanical, and wide band gap performance for high-power and extreme environment applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Total New Allotropes Identified | 87 | Structures | Monoclinic symmetry, 3D sp3 Si |
| Direct/Quasi-Direct Band Gap | 13 | Allotropes | Promising for optoelectronics |
| Metallic Allotropes | 12 (13.79%) | Allotropes | Exhibiting Fermi level crossing |
| Semiconductor Allotropes | 75 (86.36%) | Allotropes | Strong visible light absorption |
| Bulk Modulus Range (New Si) | 42 to 99 | GPa | Voigt-Reuss-Hill approximation |
| Max Bulk Modulus (Allotrope 13-3-12-232508) | 99 | GPa | Exceeds diamond Si (88 GPa) |
| Max Shear Modulus (Allotrope 15-3-24-232448) | 66 | GPa | Exceeds diamond Si (64 GPa) |
| Band Gap Range (Optoelectronic Candidates) | 1.0 to 1.91 | eV | Ideal for solar cells (1.0-1.5 eV) |
| Plane Wave Energy Cut-off | 340 | eV | DFT calculations (CASTEP) |
| k-point Grids | ~2Ï x 0.025 | Ă -1 | Monkhorst-Pack meshes |
Key Methodologies
Section titled âKey MethodologiesâThe research employed a high-throughput computational screening approach utilizing Density Functional Theory (DFT) combined with a random structure generation strategy (RG2).
- Structure Generation (RG2): A random strategy combined with group and graph theory was used to generate 15,669 initial structures within the monoclinic space group range (3-15).
- Initial Filtering: Structures were filtered based on geometric acceptability, 4-coordinated networks, and removal of two-dimensional structures, resulting in 389 unique 3D sp3 monoclinic Si allotropes.
- Geometry Optimization (DFT): Optimization was performed using the Cambridge series total energy package (CASTEP).
- Functional: Perdew-Burke-Ernzerhof (PBE) Generalized Gradient Approximation (GGA).
- Pseudopotential: Ultrasoft quasipotential (Vanderbilt).
- Minimization: Broyden-Fletcher-Goldfarb-Shanno (BFGS).
- Property Calculation: Electronic band structures were calculated using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional.
- Stability Verification:
- Mechanical Stability: Elastic constants (Cij) were calculated and verified against generalized Born mechanical stability criteria.
- Dynamic Stability: Phonon spectra were calculated using density functional perturbation theory (DFPT) to confirm the absence of negative frequencies.
- Mechanical Moduli Estimation: Bulk, Shear, and Youngâs moduli were estimated using the Voigt-Reuss-Hill approximation method.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the ongoing effort to find semiconductor materials that can match the mechanical and thermal robustness of diamond while offering superior electronic properties (direct band gap, high carrier mobility). 6CCVD specializes in the synthesis and fabrication of MPCVD Diamond, the ultimate benchmark material for extreme applications.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and ExtensionâTo benchmark the performance of these novel Si allotropes or to develop devices requiring superior properties, 6CCVD recommends the following materials from our catalog:
| 6CCVD Material | Relevance to Research | Key Advantage |
|---|---|---|
| Optical Grade SCD | Benchmark & Substrate: Provides the highest purity, widest band gap (5.5 eV), and lowest defect density for fundamental electronic and optical property comparison against the new Si allotropes. | Unmatched thermal conductivity and optical transparency (UV to IR). |
| Electronic Grade SCD | High-Power Electronics: Used for high-frequency and high-power devices where the thermal limitations of Si (even novel allotropes) are prohibitive. | Superior carrier mobility and breakdown voltage. |
| Boron-Doped Diamond (BDD) | Semiconducting/Electrochemical: BDD allows for tunable conductivity (p-type semiconductor to metallic) necessary for creating contacts or active layers in devices similar to those proposed for these Si allotropes. | Tunable band gap characteristics and extreme chemical inertness. |
| Polycrystalline Diamond (PCD) | Mechanical Benchmarking: For applications where the high bulk modulus (up to 99 GPa) of the new Si allotropes is critical, PCD offers superior hardness and mechanical stability (Bulk Modulus typically >440 GPa). | Large area plates (up to 125mm) with high mechanical strength. |
Customization Potential for Device Integration
Section titled âCustomization Potential for Device IntegrationâThe transition of these theoretical Si allotropes into functional devices requires precise material engineering and integration capabilities, which 6CCVD provides:
- Custom Dimensions: 6CCVD offers plates and wafers in custom dimensions, including large-area PCD up to 125mm, necessary for scaling up research findings into practical devices.
- Precision Thickness Control: We provide SCD and PCD layers with thickness control from 0.1 ”m up to 500 ”m, crucial for optimizing the active layer thickness in photovoltaic or optoelectronic devices.
- Advanced Metalization Services: To facilitate electrical contact and device integration (e.g., for testing carrier effective masses or band gap structures), 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition. This is essential for creating reliable contacts on novel semiconductor structures.
- Surface Preparation: Our advanced polishing techniques achieve ultra-smooth surfaces (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), minimizing scattering losses and maximizing performance in optical and electronic devices.
Engineering Support
Section titled âEngineering SupportâThe computational results demonstrate that certain Si allotropes can surpass diamond Si in specific metrics (e.g., bulk modulus, direct band gap, low electron effective mass). However, diamond remains the gold standard for overall thermal and mechanical performance.
- Benchmarking Expertise: 6CCVDâs in-house PhD engineering team specializes in comparing and contrasting the performance of conventional semiconductors (like Si) against MPCVD Diamond. We can assist researchers in selecting the optimal diamond material for high-performance Photovoltaic and Optoelectronic projects.
- Material Selection Consultation: We provide expert guidance on utilizing BDD to create conductive layers or contacts necessary for testing novel semiconductor structures, ensuring compatibility with extreme processing conditions.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) to deliver custom diamond materials directly to research facilities worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A total of 87 new monoclinic silicon allotropes are systematically scanned by a random strategy combined with group and graph theory and high-throughput calculations. The new allotropes include 13 with a direct or quasi-direct band gap and 12 with metallic characteristics, and the rest are indirect band gap semiconductors. More than 30 of these novel monoclinic Si allotropes show bulk moduli greater than or equal to 80 GPa, and three of them show even greater bulk moduli than diamond Si. Only two of the new Si allotropes show a greater shear modulus than diamond Si. The crystal structures, stability (elastic constants, phonon spectra), mechanical properties, electronic properties, effective carrier masses and optical properties of all 87 Si monoclinic allotropes are studied in detail. The electron effective masses m l of five of the new allotropes are smaller than that of diamond Si. All of these novel monoclinic Si allotropes show strong absorption in the visible spectral region. Taken together with their electronic band gap structures, this makes them promising materials for photovoltaic applications. These investigations greatly enrich the current knowledge of the structure and electronic properties of silicon allotropes.