Boron Arsenide Research Articles

The accuracy measurement of carrier mobility of cubic boron arsenide

The accuracy measurement of carrier mobility of cubic boron arsenide

Thermal Conductivity of BAs under Pressure

AbstractThe thermal conductivity of boron arsenide (BAs) is believed to be influenced by phonon scattering selection rules due to its special phonon dispersion. Compression of BAs leads to significant changes in phonon dispersion, which allows for a test of first principles theories for how phonon dispersion affects three‐ and four‐phonon scattering rates. This study reports the thermal conductivity of BAs from 0 to 30 GPa. Thermal conductivity vs. pressure of BAs is measured by time‐domain thermoreflectance with a diamond anvil cell. In stark contrast to what is typical for nonmetallic crystals, BAs is observed to have a pressure independent thermal conductivity below 30 GPa. The thermal conductivity of nonmetallic crystals typically increases upon compression. The unusual pressure independence of BAs's thermal conductivity shows the important relationship between phonon dispersion properties and three‐ and four‐phonon scattering rates.

High ambipolar mobility in cubic boron arsenide.

Semiconductors with high thermal conductivity and electron-hole mobility are of great importance for electronic and photonic devices as well as for fundamental studies. Among the ultrahigh-thermal conductivity materials, cubic boron arsenide (c-BAs) is predicted to exhibit simultaneously high electron and hole mobilities of >1000 centimeters squared per volt per second. Using the optical transient grating technique, we experimentally measured thermal conductivity of 1200 watts per meter per kelvin and ambipolar mobility of 1600 centimeters squared per volt per second at the same locations on c-BAs samples at room temperature despite spatial variations. Ab initio calculations show that lowering ionized and neutral impurity concentrations is key to achieving high mobility and high thermal conductivity, respectively. The high ambipolar mobilities combined with the ultrahigh thermal conductivity make c-BAs a promising candidate for next-generation electronics.

High ambipolar mobility in cubic boron arsenide revealed by transient reflectivity microscopy.

Semiconducting cubic boron arsenide (c-BAs) has been predicted to have carrier mobility of 1400 square centimeters per volt-second for electrons and 2100 square centimeters per volt-second for holes at room temperature. Using pump-probe transient reflectivity microscopy, we monitored the diffusion of photoexcited carriers in single-crystal c-BAs to obtain their mobility. With near-bandgap 600-nanometer pump pulses, we found a high ambipolar mobility of 1550 ± 120 square centimeters per volt-second, in good agreement with theoretical prediction. Additional experiments with 400-nanometer pumps on the same spot revealed a mobility of >3000 square centimeters per volt-second, which we attribute to hot electrons. The observation of high carrier mobility, in conjunction with high thermal conductivity, enables an enormous number of device applications for c-BAs in high-performance electronics and optoelectronics.

Vacancy induced magnetism and electronic structure modification in monolayer hexagonal boron arsenide: A first-principles study

The effect of 0D vacancy defects on the structural, electronic, magnetic, and optical properties of dynamically stable hexagonal boron arsenide monolayer was comprehensively studied using first-principles calculations. Five configurations of 0D vacancy defects — single boron vacancy, double boron vacancy, single arsenic vacancy, double arsenic vacancy, and single boron-single arsenic vacancy, were considered. Our density functional theory calculations indicated that arsenic vacancy induced magnetism (1.0 μB) in the boron atoms around the vacancy site, whereas induced magnetism was absent for other vacancy defects. The magnitude of the induced magnetic moment for arsenic vacancy decreased with the increasing concentration of vacancy. Semiconductor to metal transition was noticed due to the introduction of single boron vacancy, double boron vacancy and double arsenic vacancy. Single boron–arsenic vacancy decreased the pristine band gap though finite band gap remained. Instigating 0D vacancy modified the optical absorption spectra of the monolayer. Work function calculations revealed that the work function increased after vacancy defect was introduced. This work will be beneficial to ascertain the multifunctionality of the defective boron arsenide monolayer as 2D nanomaterials for optoelectronic and spintronic applications.

Peak thermal conductivity measurements of boron arsenide crystals

Recent experiments have validated prior theories of unusual high thermal conductivity $(\ensuremath{\kappa})$ in boron arsenide (BAs) and revealed large $\ensuremath{\kappa}$ variation associated with extended and point defects in the samples. The peak $\ensuremath{\kappa}$ provides valuable insights into the competition between intrinsic phonon-phonon scattering processes and extrinsic boundary and defect scattering processes in BAs. However, prior measurement methods have not been able to measure the peak $\ensuremath{\kappa}$ because of fundamental and technical limitations. Here, we report peak $\ensuremath{\kappa}$ measurements of BAs crystals synthesized under different conditions with source materials of different purities via a vapor transport method. For three representative samples, the measured $\ensuremath{\kappa}$ peak appears at temperatures between 120 and 150 K and varies from $410\ifmmode\pm\else\textpm\fi{}60\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ to $830\ifmmode\pm\else\textpm\fi{}100\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. The measured thermal conductivities agree with theoretical calculations across the full temperature range. The similar calculated and measured peak temperatures helps to narrow down the boundary scattering mean free path to be around 4 \ensuremath{\mu}m in two samples and 5 \ensuremath{\mu}m in another, while the variation of the peak magnitude reveals a one-order-of-magnitude difference in the strength of point defect scattering. The phonon-defect scattering behavior correlates well with the measured electronic Raman scattering background, the impurity concentrations revealed by secondary ion mass spectroscopy, and the Hall concentration and mobility of the $p$-type samples except for an anomalously high hole concentration that appears in one sample, which indicates nonuniform impurity distribution. The observed correlation clarifies the origins of extrinsic phonon scattering mechanisms in BAs crystals.

Theoretical design of BAs/WX2 (X = S, Se) heterostructures for high-performance photovoltaic applications from DFT calculations

In this paper, based on first principle calculations, we systematically investigate thermal, mechanical, electronic and optical properties of heterostructures composed of boron arsenide (BAs) and WX2 (X = S, Se). The binding energy (289.7 meV and 484.6 meV for BAs/WS2 and BAs/WSe2, respectively), phonon spectra, molecular dynamics and elastic deformation resistance indicate that the heterostructures are structurally, dynamically, and mechanically stable. The investigated van der Waals (vdWs) heterostructures (BAs/WS2 and BAs/WSe2) are all direct bandgap (0.6 eV and 0.7 eV, respectively) semiconductors, where the BAs/WS2 vdWs heterostructure possesses a type-II band alignment, which promotes the separation of photogenerated carriers and prolong their lifetime significantly. The BAs/WSe2 vdWs heterostructure exhibits a type-I band alignment, which in turn facilitates the rapid recombination of photogenerated carriers. Both BAs/WS2 and BAs/WSe2 heterostructures possess high carrier mobility (102 ∼ 103 cm2/Vs) and optical absorptivity (∼105 cm−1) in a wide range from ultraviolet to visible light region, making them highly efficient for solar energy. The band structures and carrier mobilities of BAs/WX2 heterostructures are significantly affected by the spin–orbit coupling (SOC) effect. In addition, the external electric field can tailor the band structures including the transition between the direct and the indirect band gaps and the evolution between the type-I and type-II band alignments. The theoretical predictions suggest that BAs/WX2 heterostructures are promising candidates for future nanoelectronics and optoelectronic devices, providing some valuable information for future experimental research.

Ultraweak electron-phonon coupling strength in cubic boron arsenide unveiled by ultrafast dynamics

We report a time-resolved ultrafast quasiparticle dynamics investigation of cubic boron arsenide ($c$-BAs), which is a recently discovered highly thermally conducting material. The excited-state ultrafast relaxation channels dictated by the electron-phonon coupling (EPC), phonon-phonon scattering, and radiative electron-hole recombination have been unambiguously identified, along with their typical interaction times. Significantly, the EPC strength is obtained from the dynamics, with a value of ${\ensuremath{\lambda}}_{{T}_{2}}=0.008$ (corresponding to $\ensuremath{\lambda}\ensuremath{\langle}{\mathrm{\ensuremath{\Omega}}}^{2}\ensuremath{\rangle}=1.18\ifmmode\pm\else\textpm\fi{}0.08\phantom{\rule{0.16em}{0ex}}\mathrm{p}{\mathrm{s}}^{--2}$), demonstrating an unusually weak coupling between the electrons and phonons. As a comparison, an ultraweak EPC strength for graphene is also expected. We propose that preserving an ultrasmall EPC strength may be a prerequisite for exhibiting an ultrahigh thermal conductivity. Our investigation provides insight for searching and designing ultrahigh thermal conductivity materials. Notably, during our analysis we have generalized the fluence-dependence method for obtaining the EPC strength to room temperature, which can be applied to many other types of quantum materials in the future.

Unveiling the Role of Charge Transfer in Enhanced Electrochemical Nitrogen Fixation at Single-Atom Catalysts on BX Sheets (X = As, P, Sb).

To tune single-atom catalysts (SACs) for effective nitrogen reduction reaction (NRR), we investigate various transition metals implanted on boron-arsenide (BAs), boron-phosphide (BP), and boron-antimony (BSb) using density functional theory (DFT). Interestingly, W-BAs shows high catalytic activity and excellent selectivity with an insignificant barrier of only 0.05 eV along the distal pathway and a surmountable kinetic barrier of 0.34 eV. The W-BSb and Mo-BSb exhibit high performances with limiting potentials of -0.19 and -0.34 V. The Bader-charge descriptor reveals that the charge transfers from substrate to *NNH in the first protonation step and from *NH3 to substrate in the last protonation step, circumventing a big hurdle in NRR by achieving negative free energy change of *NH2 to *NH3. Furthermore, machine learning (ML) descriptors are introduced to reduce computational cost. Our rational design meets the three critical prerequisites of chemisorbing N2 molecules, stabilizing *NNH, and destabilizing *NH2 adsorbates for high-efficiency NRR.

Strong four-phonon scattering in monolayer and hydrogenated bilayer BAs with horizontal mirror symmetry

Recently, the important role of high-order anharmonic phonon–phonon interactions has been revealed in several materials, such as cubic boron arsenide (BAs), in which the wide phononic energy gap is found to be a critical factor causing the importance of four-phonon scattering. In this work, by solving the Boltzmann transport equation, we show that the four-phonon scattering has a significant impact on the thermal transport in honeycomb structured monolayer BAs (m-BAs) and its hydrogenated bilayer counterparts (bi-BAs). The lattice thermal conductivity (κL) values of all these structures are reduced after considering four-phonon scattering. Particularly, a huge drop in κL as large as 80% is observed for m-BAs compared to the case without four-phonon scattering, which is mainly caused by the suppression of phonon lifetimes. More interestingly, as opposed to the case of graphene, κL of m-BAs is abnormally lower than its bi-BAs counterparts, which is attributed to the much larger phonon scattering rate in m-BAs compared to that in bi-BAs. By further comparing BAs sheets with and without horizontal mirror symmetry, it is found that the contribution of flexural acoustic phonon exhibits most significant reduction in both mi-BAs and bi-BAs with horizontal mirror symmetry after including four-phonon scattering. This work provides physical understanding of the role of mirror symmetry and high-order phonon scattering on the thermal transport in two-dimensional materials.

Effect of intrinsic defects on the electronic structure and thermoelectricity of two-dimensional boron arsenide

Systematic study of the two-dimensional (2D) BAs in the inherent defects on the material electronic structure (by using effective band structure), magnetic properties and thermoelectric properties of the impact by means of density general function theory (DFT) calculations. The inversion defect of the As atom replacing the B atom retains the semiconductor properties, other defects all cause the material to exhibit metallic properties. The vacancy defects and interstitial defects makes the system introduce magnetism, the magnetic originate mainly from the s and p orbitals of the atoms near the defects, and the contribution of the d orbital is almost negligible. Novelty is that the defect of a B atom replacing an As atom significantly improves the thermoelectric performance of the system. The results provide the basis for the application of 2D BAs in magnetic materials, microelectronic devices and thermoelectric materials.

Detecting the Knowledge Domains of Compound Semiconductors.

The development of compound semiconductors (CS) has received extensive attention worldwide. This study aimed to detect and visualize CS knowledge domains for quantifying CS research patterns and emerging trends through a scientometric review based on the literature between 2011 and 2020 by using CiteSpace. The combined dataset of 24,622 bibliographic records were collected through topic searches and citation expansion to ensure adequate coverage of the field. While research in “solar cell” and “perovskite tandem” appears to be the two most distinctive knowledge domains in the CS field, research related to thermoelectric materials has grown at a respectable pace. Most notably, the deep connections between “thermoelectric material” and “III-Sb nanowire (NW)” research have been demonstrated. A rapid adaptation of black phosphorus (BP) field-effect transistors (FETs) and gallium nitride (GaN) transistors in the CS field is also apparent. Innovative strategies have focused on the opto-electronics with engineered functionalities, the design, synthesis and fabrication of perovskite tandem solar cells, the growing techniques of Sb-based III–V NWs, and the thermal conductivity of boron arsenide (BAs). This study revealed how the development trends and research areas in the CS field advance over time, which greatly help us to realize its knowledge domains.

Accurate description of high-order phonon anharmonicity and lattice thermal conductivity from molecular dynamics simulations with machine learning potential

Phonon anharmonicity is critical for accurately predicting the material's thermal conductivity ($\ensuremath{\kappa}$). However, its calculation based on the perturbation theory is a difficult and time-consuming task, especially for the high-order phonon scattering process. In this work, using cubic boron arsenide (BAs) and diamond as examples, we combine the machine learning potential (MLP) with molecular dynamics simulations to predict $\phantom{\rule{4pt}{0ex}}\ensuremath{\kappa}$ and assess the effect of anharmonicity on thermal transport properties. A MLP based on the matrix tensor algorithm is developed in this work, which can accurately describe lattice dynamics behaviors in both BAs and diamond. The phonon spectral energy density analysis reveals that MLP can effectively capture both the phonon mode softening and the linewidth broadening induced by the anharmonicity at finite temperatures in both materials. Compared to diamond, BAs exhibits a stronger anharmonicity revealed by the larger deviation from equilibrium position and more pronounced phonon broadening effect, especially at high temperatures. Furthermore, based on the phonon Boltzmann transport equation and three-phonon scattering process, our calculation results demonstrate that the accuracy of the MLP in predicting the $\ensuremath{\kappa}$ is comparable to that of density-functional theory calculations for both diamond and BAs. However, this framework can only predict $\ensuremath{\kappa}$ of diamond in agreement with experimental measurements, but significantly overestimates the $\ensuremath{\kappa}$ of BAs compared to the experimental results, due to the significant impact of high-order phonon scattering process in BAs. In contrast, the $\ensuremath{\kappa}$ values predicted by equilibrium molecular dynamics simulations combined with MLP agree well with experimental values for both BAs and diamond. Our study suggests that molecular dynamics simulation combined with MLP is a reliable and computationally efficient tool to account for full orders of anharmonicity and provide accurate predictions of material's thermal conductivity without any a priori knowledge of the importance of high-order phonon anharmonicity.

Recent progress on cubic boron arsenide with ultrahigh thermal conductivity

Predictions of ultrahigh thermal conductivity in boron arsenide using first-principles calculations have motivated research to synthesize crystals and investigate their properties. In 2018, three groups reported synthesizing small single crystals of boron arsenide that exhibit thermal conductivity of 700–1300 W m−1 K−1 at room temperature. The progress in crystal growth has attracted significant attention and has inspired additional theoretical and experimental research. This brief review provides an overview of recent theoretical and experimental studies on boron arsenide, mostly since 2018. Progress in theoretical calculations, synthesis methods, characterizations, physical properties, and potential applications are presented, followed by a discussion of the remaining challenges and outlook for boron arsenide research.

Vacancy Induced Magnetism and Electronic Structure Modification in Monolayer Hexagonal Boron Arsenide: A First-Principles Study

Vacancy Induced Magnetism and Electronic Structure Modification in Monolayer Hexagonal Boron Arsenide: A First-Principles Study

Finite-momentum excitons and the role of electron-phonon couplings in the electronic and phonon transport properties of boron arsenide.

The emerging semiconductor boron arsenide (BAs) with high thermal conductivity has attracted much attention recently, due to its promising application to overcome the bottleneck of high-density heat generated in power electronics and optoelectronic devices. In this work, based on first-principles calculations, we find that cubic BAs possesses high intrinsic electron/hole mobilities and the ionized impurity scattering plays a more important role in carrier scattering, compared with other scattering processes. The mobilities can be significantly enhanced by 14.9% and 76.2% for electrons and holes, respectively, by strain engineering. The investigation of the optoelectronic properties of indirect semiconductor cubic BAs by considering the many-body excitonic effects reveals that the contribution from finite-momentum excitons to optical properties is larger for photon energy ranging from 2.25 eV to 3.50 eV, compared with that from zero-momentum excitons. Finally, we observe that the phonon-electron couplings to total lattice thermal conductivities are non-trivial at low temperatures. These findings provide new insight into the transport and optoelectronic properties of cubic BAs, which are beneficial for the acceleration of the application of this revolutionary thermal management material.

Abnormal enhancement of thermal conductivity by planar structure: A comparative study of graphene-like materials

The traditional knowledge that the lone-pair electrons lead to low thermal conductivity provides important clues for the prediction of thermal conductivity and fundamental understanding on phonon transport. In this study, we reported a counterintuitive phenomenon that the thermal conductivity can increase by up to two orders of magnitude after activating the lone-pair electrons. Boron atoms are introduced to the two-dimensional (2D) nitrogene, blue phosphorene, arsenene, and antimonene to activate the lone-pair electrons, i.e., graphene-like boron nitride (g-BN), boron phosphide (g-BP), boron arsenide (g-BAs), and boron antimonide (g-BSb). This phenomenon is intuitively reflected in the competitive effect of phonon thermal transport (1) between in-plane and out-of-plane acoustic phonon modes, (2) between Grüneisen parameter and scattering phase space, and (3) between unbonded s-electrons pair and their space appearance. The essence of competition lies in the feedback adjustment of the structure to the electronic distribution, which reflects the high sensitivity of the thermal conductivity on the structure and overcomes the strong anharmonicity caused by the lone-pair electrons. Our study provides a counterexample to the traditional model of low thermal conductivity caused by lone-pair electrons. The results reported in this study provide a new perspective on the thermal transport, which is helpful to understand the key role of structure in phonon thermal transport in 2D materials.

Stronger three-phonon interactions revealed by molecular dynamics in materials with restricted phase space

Utilizing molecular dynamics (MD) simulations based on the highly precise force-fields, we find that phonon scattering strengths induced by the cubic anharmonicity can be significantly underestimated by the perturbation theory (PT) approach in materials with sizable frequency gaps or branch bunching. We trace this result to the additional three-phonon scatterings in MD enabled by the fluctuating phonon energy and the continuous energy exchange between modes. These channels are essential to accurately evaluate the zone-center phonon linewidth in boron arsenide as compared to the experiment and could noticeably lower the lattice thermal conductivity of beryllium telluride and tungsten carbide. Accordingly, due to the stronger three-phonon scatterings, four-phonon scatterings would become less important than previously believed in this type of material. Moreover, our work emphasizes the different phonon scattering processes in MD and PT simulations, offering new insights for an improved description of anharmonic properties.

Surface-Functionalized Boron Arsenide as a Photocathode for CO2 Reduction

Surface-Functionalized Boron Arsenide as a Photocathode for CO₂ Reduction

Design and Optimization of a Composite Heat Spreader to Improve the Thermal Management of a Three-Dimensional Integrated Circuit

Abstract This study establishes a numerical investigation of the optimal distribution of a limited amount of high thermal conductivity material to enhance the heat removal from 3D integrated circuits, IC. The structure of the heat spreader is designed as a composite of high thermal conductivity (Boron Arsenide) and moderate thermal conductivity (copper) materials. The volume ratio of high-conductivity inserts to the total volume of the spreader is set at a fixed pertinent ratio. Two different boundary conditions of constant and variable temperature are considered for the heat sink. To examine the impact of adding high-conductivity inserts on the cooling performance of the heat spreader, various patterns of the single and double ring inserts are studied. A parametric study is performed to find the optimal location of the rings. Moreover, the optimal distribution of the high-conductivity material between the inner and outer rings is found. The results show that for the optimal conditions, the maximum temperature of the 3D IC is reduced up to 10%; while at the same time, the size of the heat sink and heat spreader can be diminished by as much as 200%.