BC8 Silicon (Si-III) is a Narrow-Gap Semiconductor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-04-03 |
| Journal | Physical Review Letters |
| Authors | Haidong Zhang, Hanyu Liu, Kaya Wei, Oleksandr O. Kurakevych, Yann Le Godec |
| Institutions | Sorbonne Université, National Institute of Standards and Technology |
| Citations | 75 |
| Analysis | Full AI Review Included |
BC8 Silicon: A Narrow-Gap Semiconductor - 6CCVD Technical Analysis
Section titled âBC8 Silicon: A Narrow-Gap Semiconductor - 6CCVD Technical AnalysisâThis document analyzes the research findings regarding BC8 Silicon (Si-III) and outlines how 6CCVDâs advanced MPCVD diamond materials and customization capabilities can support and extend research in narrow-gap semiconductors, mid-IR plasmonics, and extreme thermal management.
Executive Summary
Section titled âExecutive Summaryâ- Fundamental Redefinition: The research conclusively demonstrates that BC8-Si is an ultra-narrow direct band gap semiconductor (Eg ~30 meV), contradicting previous classifications as a semimetal.
- Mid-IR Plasmonics Potential: The material exhibits a plasma wavelength (λp) near 11.1 ”m, positioning BC8-Si as a promising platform for mid-infrared (mid-IR) plasmonic devices, an area traditionally challenging for conventional noble metals.
- Extreme Thermal Properties: BC8-Si shows a thermal conductivity (Îș) that is 1-2 orders of magnitude lower than standard diamond cubic silicon (DC-Si), making it highly relevant for thermoelectric and thermal barrier applications.
- Electrical Transport: Room temperature electrical conductivity is measured at 76 S/cm, with a negative Seebeck coefficient (-6 ”V/K), confirming electron-dominated semiconducting behavior.
- Synthesis Requirement: Reliable characterization was enabled by the successful synthesis of homogeneous, phase-pure bulk samples, highlighting the need for precise material control in advanced semiconductor research.
- 6CCVD Value Proposition: While BC8-Si is a silicon allotrope, the applications explored (mid-IR optics, high-performance semiconductors, thermal management) are core strengths of MPCVD diamond. 6CCVD offers superior Single Crystal Diamond (SCD) for optical transparency and Boron-Doped Diamond (BDD) for tunable electronic properties in extreme environments.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the characterization of phase-pure BC8-Si bulk samples:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Band Gap (Eg) | 30 ± 3 | meV | Direct band gap, derived from Far-IR Tauc plot analysis |
| Plasma Wavelength (λp) | 11.1 | ”m | Mid-IR reflectivity, indicative of mobile charge carriers |
| Electrical Conductivity (Ï) | 76 | S/cm | Measured at 300 K (Room Temperature) |
| Carrier Density (n) | ~4.6 x 1018 | cm-3 | Estimated at 300 K |
| Carrier Mobility (”) | ~93 | cm2/(V·s) | Estimated at 300 K |
| Thermal Conductivity (Îș) | 20 - 35 | W/(m·K) | Range between 300 K and 125 K |
| Seebeck Coefficient (S) | -6 | ”V/K | Measured at 300 K (Negative sign indicates electron dominance) |
| Debye Temperature (Ξ) | 517 ± 6 | K | Derived from low-temperature heat capacity |
| Lattice Parameter (a) | 6.62767(3) | Ă | Experimental unit cell parameter |
Key Methodologies
Section titled âKey MethodologiesâThe successful characterization relied on synthesizing phase-pure bulk samples and employing a suite of advanced measurement techniques:
- Synthesis (HPHT): Bulk samples of BC8-Si were synthesized via direct transformation of elemental silicon using the multi-anvil press method.
- Alternative Synthesis: Phase-pure âchemical samplesâ were obtained at 9.5 GPa in the Na-Si system.
- Structural Verification: Homogeneity and phase purity were confirmed using X-ray diffraction, Raman spectroscopy, and nuclear magnetic resonance spectroscopy.
- Optical Characterization:
- Far-IR optical transmittance measurements were used to determine the fundamental band edge transition (~240 cm-1).
- Room-temperature optical reflectivity in the mid-IR regime identified a plasma edge near 900 cm-1.
- Electrical Transport: Four-probe electrical conductivity measurements were performed across a wide temperature range (300 K down to 12 K) to determine semiconducting behavior and activation energy.
- Thermoelectric Analysis: First-time measurements of thermal conductivity (Îș) and Seebeck coefficient (S) were conducted to characterize thermal transport properties.
- Computational Modeling: Density Functional Theory (DFT) calculations, utilizing hybrid HSE06 functionals with adjusted Hartree-Fock (HF) exchange mixing (up to 35%), were used to computationally reproduce the ultra-narrow band gap.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research on BC8-Si highlights the critical need for advanced materials with tailored optical, electronic, and thermal properties for next-generation devices (e.g., mid-IR plasmonics, high-efficiency thermoelectrics). 6CCVDâs MPCVD diamond materials offer superior performance and customization capabilities that directly address these engineering challenges.
Applicable Materials for Advanced Semiconductor Research
Section titled âApplicable Materials for Advanced Semiconductor ResearchâWhile BC8-Si offers unique low thermal conductivity, 6CCVD provides materials that excel in complementary extreme environments, particularly where high thermal stability, optical transparency, or tunable conductivity are paramount.
| Application Focus | 6CCVD Material Recommendation | Key Benefit over BC8-Si/DC-Si |
|---|---|---|
| Mid-IR Optics & Plasmonics | Optical Grade SCD | Zero absorption across the entire mid-IR spectrum (superior to Si). Highest purity (N < 1 ppm) for minimal scattering losses. |
| High-Power Electronics/Heat Spreading | High Thermal Conductivity SCD | Thermal conductivity up to 2200 W/(m·K) (50x higher than BC8-Si), essential for managing heat in high-density devices. |
| Electrochemistry & Tunable Semiconductors | Heavy Boron-Doped Diamond (BDD) | Highly stable, p-type semiconductor with tunable conductivity (from insulating to metallic). Ideal for extreme chemical/radiation environments. |
| Large-Area Device Integration | Polycrystalline Diamond (PCD) | Available in large formats (up to 125mm diameter) with excellent thermal and mechanical properties for wafer-scale processing. |
Customization Potential for Replication and Extension
Section titled âCustomization Potential for Replication and ExtensionâThe synthesis of BC8-Si required precise control over bulk material properties. 6CCVD offers the necessary customization to support similar high-precision material science projects:
- Custom Dimensions: We provide SCD and PCD plates/wafers up to 125mm in diameter, allowing researchers to move beyond micron-scale samples (a limitation noted in the paper) to bulk, phase-pure material studies.
- Thickness Control: SCD and PCD layers can be grown from 0.1 ”m up to 500 ”m thick, providing flexibility for thin-film optical studies or robust bulk thermal measurements. Substrates up to 10mm thick are available.
- Surface Engineering: We offer ultra-smooth polishing down to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, critical for minimizing scattering losses in optical and plasmonic applications (like those discussed for BC8-Si).
- Integrated Metalization: The development of advanced devices often requires specific contact layers. 6CCVD offers in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu, tailored to the specific contact requirements of novel semiconductor structures.
Engineering Support
Section titled âEngineering SupportâThe successful characterization of BC8-Si relied heavily on resolving controversial experimental data through precise material synthesis and advanced measurement. 6CCVD understands the challenges inherent in working with exotic materials.
- Consultation: 6CCVDâs in-house PhD team specializes in the electronic, optical, and thermal properties of wide-bandgap materials. We can assist researchers in material selection, doping levels (for BDD), and surface preparation for similar mid-IR plasmonics and extreme environment semiconductor projects.
- Global Logistics: We ensure reliable, global delivery of sensitive materials, with DDU (Delivered Duty Unpaid) as the default and DDP (Delivered Duty Paid) options available.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Large-volume, phase-pure synthesis of BC8 silicon (Ia3[over ÂŻ], cI16) has enabled bulk measurements of optical, electronic, and thermal properties. Unlike previous reports that conclude BC8-Si is semimetallic, we demonstrate that this phase is a direct band gap semiconductor with a very small energy gap and moderate carrier concentration and mobility at room temperature, based on far- and midinfrared optical spectroscopy, temperature-dependent electrical conductivity, Seebeck and heat capacity measurements. Samples exhibit a plasma wavelength near 11 ÎŒm, indicating potential for infrared plasmonic applications. Thermal conductivity is reduced by 1-2 orders of magnitude depending on temperature as compared with the diamond cubic (DC-Si) phase. The electronic structure and dielectric properties can be reproduced by first-principles calculations with hybrid functionals after adjusting the level of exact Hartree-Fock (HF) exchange mixing. These results clarify existing limited and controversial experimental data sets and ab initio calculations.