High thermal conductivity driven by the unusual phonon relaxation time platform in 2D monolayer boron arsenide
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | RSC Advances |
| Authors | Yanxiao Hu, Dengfeng Li, Yan Yin, Shichang Li, Hangbo Zhou |
| Institutions | Chongqing University of Posts and Telecommunications, A*STAR Graduate Academy |
| Citations | 24 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the diffusive thermal transport properties of two-dimensional (2D) monolayer honeycomb Boron Arsenide (h-BAs) using first-principles calculations and the Boltzmann Transport Equation (BTE).
- High Thermal Conductivity (TC): Monolayer h-BAs exhibits an ultra-high TC of 181 W m-1 K-1 at 300 K, positioning it as a leading thermally conductive 2D semiconductor.
- Dominant Heat Carriers: Unlike graphene and h-BN, where out-of-plane acoustic (ZA) phonons dominate TC, h-BAs heat transport is primarily driven by in-plane acoustic (IA) modes (76% contribution).
- Unique Relaxation Platform: The high TC is attributed to an unusual frequency-independent âplatformâ region observed in the relaxation time of IA phonons, extending relaxation times up to 102 ps.
- Scattering Suppression Mechanism: This platform results from the suppression of key three-phonon scattering channels (specifically ZA + ZA â IA) due to the extremely flat dispersion of the ZA phonon branch in h-BAs.
- Comparative Advantage: h-BAs TC is approximately one order of magnitude higher than that of h-GaN (16 W m-1 K-1), despite similar mass densities, highlighting the critical role of phonon spectrum differences.
- Physical Insight: The low TC of h-GaN is linked to a downward trend in its out-of-plane optical (ZO) branch, which increases the phase space for ZA + IA â ZO scattering, a mechanism suppressed in h-BAs.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Thermal Conductivity (h-BAs) | 181 | W m-1 K-1 | Iterative BTE solution at 300 K |
| Thermal Conductivity (h-GaN) | 16 | W m-1 K-1 | Iterative BTE solution at 300 K |
| IA Mode Contribution (h-BAs) | 76 | % | Percentage of total TC at 300 K |
| ZA Mode Contribution (h-BAs) | 23 | % | Percentage of total TC at 300 K |
| TC Ratio (h-BAs / h-GaN) | >10 | - | Comparison at 300 K |
| Lattice Constant (h-BAs) | 3.39 | A | Optimized structure |
| LO-TO Frequency Gap | 0.31 | THz | Splitting at Gamma (Î) point |
| Maximum ZA Frequency | 1.81 | THz | Indicates weak out-of-plane vibration |
| LA Group Velocity (Long-wave) | 9.3 x 103 | m s-1 | Longitudinal Acoustic branch limit |
| Born Effective Charge (B, in-plane) | 1.744 | e | Z*(B)xx |
| Born Effective Charge (B, out-of-plane) | -0.051 | e | Z*(B)zz (Indicates minimal charge transfer) |
| Dielectric Constant (In-plane) | 4.678 | - | Δxx |
| Dielectric Constant (Out-of-plane) | 1.162 | - | Δzz |
Key Methodologies
Section titled âKey MethodologiesâThe thermal properties were determined using computational physics methods based on Density Functional Theory (DFT) and the phonon Boltzmann Transport Equation (BTE).
- DFT Calculation: Performed using the Vienna Ab initio Simulation Package (VASP) employing the Generalized Gradient Approximation (GGA) functional (PBE).
- Structural Optimization: The structure was fully relaxed with a kinetic energy cutoff of 550 eV. Relaxation continued until the interatomic force was less than 10-5 eV A-1.
- Electronic Convergence: Energy convergence criteria were set to 10-7 eV, utilizing a Î-centered k-mesh of 21 x 21 x 1 for Brillouin Zone (BZ) sampling.
- Phonon BTE Solution: The ShengBTE code was used to solve the BTE, calculating thermal conductivity under both the Relaxation Time Approximation (RTA) and iterative methods.
- Interatomic Force Constants (IFCs): Both 2nd and 3rd order IFCs were calculated via the finite displacement method.
- Supercells used: 7 x 7 x 1 (for 2nd IFCs) and 3 x 3 x 1 (for 3rd IFCs).
- Interactions were considered up to the 7th nearest neighbors (cutoff distance 0.68 nm).
- Scattering Calculation: A dense 101 x 101 x 1 q-mesh was used for accurate phonon-phonon scattering calculations.
- Long-Range Correction: Born effective charges and dielectric constants were calculated using Density Functional Perturbation Theory (DFPT) to correct the dynamical matrix for long-range electrostatic interactions.
- Isotope Inclusion: Natural isotopic abundances for Boron (10B and 11B) and Arsenic (75As) were included in the scattering rate calculations.
Commercial Applications
Section titled âCommercial ApplicationsâThe exceptional thermal conductivity of h-BAs, combined with its semiconductor properties (reported band gap of 1.18 eV), makes it highly promising for thermal management in advanced microelectronic and optoelectronic systems.
- Thermal Management in Integrated Circuits (ICs): Utilizing h-BAs as an ultra-efficient 2D heat spreader or substrate layer to dissipate localized heat in highly miniaturized, high-power density electronic devices.
- High-Frequency and Power Electronics: Application in Gallium Nitride (GaN) or Silicon Carbide (SiC) based power devices where thermal bottlenecks limit performance and reliability. h-BAs could serve as a superior thermal interface material (TIM) or buffer layer.
- Optoelectronics and Lasers: Use in short-wavelength optoelectronic devices (e.g., UV LEDs or lasers) where localized heating is critical. The high TC ensures stable operating temperatures and extended device lifespan.
- Advanced Semiconductor Architectures: Integration into heterostructures or van der Waals stacks where both high carrier mobility and excellent thermal dissipation are required simultaneously.
- Thermal Interface Materials (TIMs): Development of h-BAs nanoflakes or films for use in high-performance TIMs, replacing conventional materials like graphene or h-BN in demanding thermal applications.
View Original Abstract
The cubic boron arsenide (BAs) crystal has received extensive research attention because of its ultra-high thermal conductivity comparable to that of diamond.