Helium incorporation induced direct-gap silicides
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2021-06-10 |
| Journal | npj Computational Materials |
| Authors | Shicong Ding, Jingming Shi, Jiahao Xie, Wenwen Cui, Pan Zhang |
| Institutions | Liaocheng University, Jilin University |
| Citations | 12 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Direct-Gap Silicides via Helium Incorporation
Section titled āTechnical Documentation & Analysis: Direct-Gap Silicides via Helium IncorporationāThis document analyzes the research article āHelium incorporation induced direct-gap silicidesā (npj Computational Materials (2021)7:89) and connects its findings regarding advanced semiconductor materials to the core capabilities and product offerings of 6CCVD (6ccvd.com), an expert supplier of MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD).
Executive Summary
Section titled āExecutive SummaryāThe research identifies a novel pathway for creating highly efficient, direct-gap silicon (Si) allotropes suitable for thin-film photovoltaics by using Helium (He) as a temporary structural stabilizer under high pressure.
- Direct-Gap Discovery: First-principles calculations predict four dynamically stable SiāHe phases (oP36, tP9, mC18, mC12) formed under high pressure.
- Optimal Photovoltaic Match: oP36-SiāHe (1.24 eV) and mC12-SiāHe (1.34 eV) are confirmed as direct-gap semiconductors, aligning closely with the 1.34 eV Shockley-Queisser limit for maximum solar conversion efficiency (33.7%).
- Superior Absorption: The mC12-SiāHe phase exhibits a dipole-allowed direct transition and significantly higher solar absorption capacity compared to traditional cubic diamond Si (CD-Si).
- Synthesis Pathway: The proposed synthesis involves stabilizing the SiāHe host-guest structure at high pressure, followed by thermal degassing (He removal) to yield metastable, direct-gap Si allotropes (oC24-Si, tP6-Si, mC8-Si).
- 6CCVD Relevance: This work highlights the critical need for ultra-stable, high-quality thin-film materials and advanced interface engineering, areas where 6CCVDās custom MPCVD diamond (SCD and BDD) solutions offer superior performance and stability compared to metastable Si allotropes.
Technical Specifications
Section titled āTechnical SpecificationsāThe following hard data points were extracted from the computational analysis of the SiāHe phases and resulting Si allotropes:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal Band Gap (Shockley-Queisser Limit) | 1.34 | eV | Maximum solar conversion efficiency (33.7%) |
| oP36-SiāHe Band Gap | 1.24 | eV | Direct Gap (HSE06 calculation) |
| mC12-SiāHe Band Gap | 1.34 | eV | Direct Gap (HSE06 calculation), Dipole-Allowed Transition |
| oC24-Si Band Gap (Post-He Removal) | 0.95 | eV | Quasi-Direct Gap |
| mC8-Si Band Gap (Post-He Removal) | 0.84 | eV | Indirect Gap |
| He Removal Energy Barrier (tP9-SiāHe) | 0.01 | eV | Comparatively easy removal via thermal degassing |
| He Removal Energy Barrier (mC18-SiāHe) | 1.51 | eV | High barrier due to small channel diameter (3.9 Ć ) |
| Phase Transition Pressure (oP36-SiāHe to hP6-SiāHe) | 18 | GPa | Static-lattice calculation (0 K) |
| Phase Transition Pressure (oP36-SiāHe to hP6-SiāHe) | 26 | GPa | Quasi-harmonic approximation (1500 K) |
| Plane Wave Cutoff Energy | 800 | eV | DFT/VASP calculation parameter |
Key Methodologies
Section titled āKey MethodologiesāThe experimental pathway relies entirely on advanced computational material science techniques to predict stability and electronic properties under extreme conditions.
- Structural Prediction: Crystal structure searches for SiāHe were performed using the CALYPSO (Crystal structure Analysis by Particle Swarm Optimization) method at 10 GPa, maximizing eight formula units (f.u.) per simulation cell.
- Structural Optimization and DFT: Calculations were implemented using the Vienna ab initio simulation package (VASP), adopting the Perdew-Burke-Ernzerhof (PBE) functional for generalized gradient approximation (GGA).
- Band Gap Calculation: The Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional was employed to accurately correct the electronic band structures, confirming the direct-gap nature of oP36-SiāHe and mC12-SiāHe.
- Dynamic Stability Confirmation: Phonon dispersion calculations and NVT Molecular Dynamics (MD) simulations (at 0 GPa and 300 K) confirmed the dynamic and thermodynamic stability of the predicted phases.
- Migration Barrier Analysis: The Climbing Image Nudged Elastic Band (CI-NEB) method was used to calculate the energy barriers for He diffusion and removal, confirming that He atoms could be easily removed from oP36-SiāHe, tP9-SiāHe, and mC12-SiāHe.
6CCVD Solutions & Capabilities
Section titled ā6CCVD Solutions & CapabilitiesāThis research demonstrates the pursuit of advanced semiconductor materials with optimal band gaps and high absorption for thin-film applications. While the paper focuses on metastable silicon allotropes, 6CCVD provides materials that offer superior stability, thermal management, and electronic performance for next-generation devices, particularly in high-power and high-frequency domains where Si limitations are critical.
| Research Requirement/Challenge | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Applicable Materials: Direct-gap semiconductor with high absorption (mC12-SiāHe analog). | Optical Grade SCD & Heavy Boron-Doped Diamond (BDD) | SCD offers the widest band gap (5.5 eV) and highest thermal conductivity (22 W/cmĀ·K), crucial for high-power devices. BDD provides tunable p-type semiconducting properties, ideal for electrochemical and high-frequency applications, offering stability far exceeding metastable Si allotropes. |
| Customization Potential: Thin-film architecture (thin-film solar cell candidate). | Custom Dimensions and Thickness Control | 6CCVD specializes in MPCVD growth of SCD and PCD films with precise thickness control, ranging from 0.1 Āµm to 500 Āµm. This capability is essential for replicating or extending thin-film device architectures. We offer plates/wafers up to 125 mm (PCD). |
| Interface Engineering & Contact Layers: Need for precise metal contacts for device fabrication. | In-House Custom Metalization Services | We offer internal metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to define custom contact geometries and materials required for high-pressure precursors or post-degassing Si allotrope devices. |
| Material Quality for Optical Studies: Need for highly polished surfaces for accurate optical absorption measurements. | Ultra-Low Roughness Polishing | Our SCD wafers are polished to an ultra-smooth finish (Ra < 1 nm), and inch-size PCD wafers to Ra < 5 nm. This minimizes scattering losses, ensuring high fidelity for optical absorption and dielectric function measurements, similar to those performed on oP36-SiāHe and mC12-SiāHe. |
| High-Pressure/High-Temperature Substrates: Need for stable substrates for synthesis (e.g., up to 1500 K and 26 GPa). | Thick Diamond Substrates | We supply robust diamond substrates up to 10 mm thick, providing the mechanical and thermal stability required for extreme synthesis conditions (high pressure, high temperature thermal degassing) used in this research pathway. |
Engineering Support
Section titled āEngineering Supportā6CCVDās in-house team of PhD material scientists can provide expert consultation on material selection, doping levels (for BDD), and surface preparation techniques necessary for high-pressure synthesis and thermal processing projects involving novel semiconductors or host-guest structures. We offer global shipping (DDU default, DDP available) to ensure timely delivery of custom materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The search of direct-gap Si-based semiconductors is of great interest due to the potential application in many technologically relevant fields. This work examines the incorporation of He as a possible route to form a direct band gap in Si. Structure predictions and first-principles calculations show that He and Si, at high pressure, form four dynamically stable phases of Si 2 He (oP36-Si 2 He, tP9-Si 2 He, mC18-Si 2 He, and mC12-Si 2 He). All phases adopt host-guest structures consisting of a channel-like Si host framework filled with He guest atoms. The Si frameworks in oP36-Si 2 He, tP9-Si 2 He, and mC12-Si 2 He could be retained to ambient pressure after removal of He, forming three pure Si allotropes. Among them, oP36-Si 2 He and mC12-Si 2 He exhibit direct band gaps of 1.24 and 1.34 eV, respectively, close to the optimal value (~1.3 eV) for solar cell applications. Analysis shows that mC12-Si 2 He with an electric dipole transition allowed band gap possesses higher absorption capacity than cubic diamond Si, which makes it to be a promising candidate material for thin-film solar cell.