| Metadata | Details |
|---|
| Publication Date | 2025-10-14 |
| Journal | Physical review. B./Physical review. B |
| Authors | Xiao Zhang, Shashi B. Mishra, Elena R. Margine, Emmanouil Kioupakis |
| Institutions | University of Michigan, Binghamton University |
| Analysis | Full AI Review Included |
- Metastable Stability: Cubic BeB2 (c-BeB2) is confirmed to be dynamically stable under ambient conditions, despite being thermodynamically metastable relative to other BeB2 polytypes.
- High Hole Mobility: The material exhibits high intrinsic hole mobility, calculated at 1,259 cm2V-1s-1 at 300 K, which is approximately 58% of the mobility found in diamond.
- Intrinsic p-type Behavior: Defect calculations show that the Be vacancy (VBe) acts as a shallow acceptor with a negative formation energy, suggesting the material is intrinsically degenerate p-type.
- Epitaxial Integration Potential: c-BeB2 shows a close lattice match (e.g., -1.4% mismatch to 3C-SiC) with established cubic and hexagonal substrates (3C-SiC, MgO, 4H-SiC), suggesting thin-film stabilization via epitaxial growth is feasible.
- High Conductivity: At high doping levels (p = 1022 cm-3), the material achieves a high electrical conductivity of 3.08 x 106 Ω-1m-1.
- Low-Temperature Superconductor: Heavily hole-doped c-BeB2 is predicted to be a low-temperature superconductor with a critical temperature (Tc) up to 3.65 K, comparable to B-doped diamond and SiC.
| Parameter | Value | Unit | Context |
|---|
| Crystal Structure | cF12 (F43m) | N/A | Zinc blende-like cubic lattice |
| Optimized Lattice Constant | 4.297 | Angstrom | Calculated using HSE hybrid functional |
| Fundamental Band Gap (Indirect) | 1.58 | eV | Calculated using GW approximation |
| Minimum Direct Gap | 1.86 | eV | Calculated using GW approximation (at Î point) |
| Intrinsic Hole Mobility (300 K) | 1,259 | cm2V-1s-1 | Limited by hole-phonon scattering |
| Electrical Conductivity (Max) | 3.08 x 106 | Ω-1m-1 | At doping level p = 1022 cm-3 |
| Superconducting Critical Temp (Tc) | 3.65 | K | Calculated using Jellium Model (JM) at 9.8 x 1021 cm-3 |
| Light Hole Effective Mass (Î-L) | 0.059 | m0 | Very light mass, favors efficient transport |
| High-Frequency Dielectric Constant | 13.99 | N/A | Calculated using DFPT |
| Be Born Effective Charge | +2.2 | e | Indicates polar nature of Be-B bonds |
| Lattice Mismatch to 3C-SiC | -1.4 | % | Favorable for epitaxial thin-film growth |
| Zero-Point Band Gap Renormalization | 189 | meV | Due to electron-phonon interaction |
- Ground State and Structural Optimization: Density Functional Theory (DFT) calculations were performed using the Quantum Espresso (QE) package with PBE exchange-correlation functional and optimized norm-conserving Vanderbilt (ONCV) pseudopotentials.
- Electronic Structure Refinement: Band gaps and quasiparticle energies were evaluated using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional and the GW approximation (BerkeleyGW package) to account for many-body effects.
- Dynamical Stability: Phonon dispersion curves were computed using Density Functional Perturbation Theory (DFPT) to confirm the absence of imaginary phonons, verifying dynamic stability.
- Defect Analysis: Defect formation energies for intrinsic (VBe, BeB) and extrinsic (LiBe, HBe) acceptors were calculated using VASP with HSE06 hybrid functionals on 2x2x2 supercells, incorporating periodic charge corrections (Freysoldt scheme).
- Carrier Transport Modeling: Hole mobility was determined by solving the Boltzmann Transport Equation (BTE), as implemented in the EPW code. Calculations included both hole-phonon scattering and hole-ionized-impurity scattering (point charge model).
- Superconductivity Prediction: Electron-phonon coupling strength (λ) and the Eliashberg spectral function (α2F(Ï)) were calculated using DFPT. The critical temperature (Tc) was estimated using the McMillan formula, comparing results from the Rigid Band Model (RBM) and the Charge-Compensated Jellium Model (JM).
- Advanced p-type Transistors: The combination of high hole mobility and intrinsically degenerate p-type behavior makes c-BeB2 suitable for high-performance p-channel field-effect transistors (p-FETs).
- High-Speed Electronics: The light effective hole mass (as low as 0.059 m0) suggests potential for high-frequency operation and reduced power consumption in electronic devices.
- Epitaxial Power Electronics: Due to the close lattice match with SiC substrates, c-BeB2 could be integrated as a novel p-type layer in SiC-based power devices, potentially enhancing efficiency or reducing contact resistance.
- Cryogenic and Quantum Components: The predicted low-temperature superconductivity (Tc up to 3.65 K) places it in a class with B-doped diamond, making it relevant for specialized superconducting circuits and sensors operating near liquid helium temperatures.
- High-Conductivity Contacts: The high electrical conductivity achieved at high doping levels makes it a candidate for low-resistance ohmic contacts or highly conductive layers in microelectronic stacks.
View Original Abstract
Boron forms a wide variety of compounds with alkaline earth elements due to its unique bonding characteristics. Among these, binary compounds of Be and B display particularly rich structural diversity, attributed to the small atomic size of Be. Cubic BeB$_2$ is a particularly interesting phase, where Be donates electrons to stabilize a diamond-like boron network under high pressure. In this work, we employ \textit{ab initio} methods to conduct a detailed investigation of cubic BeB$_2$ and its functional properties. We show that this metastable phase is dynamically stable under ambient conditions, and its lattice match to existing substrate materials suggests possible epitaxial stabilization via thin-film growth routes. Through a comprehensive characterization of its electronic, transport, and superconductivity properties, we demonstrate that cubic BeB$_2$ exhibits high hole concentrations and high hole mobility, making it a potential candidate for efficient $p$-type transport. In addition, cubic BeB$_2$ is found to exhibit low-temperature superconductivity at degenerate doping levels, similar to several other doped covalent semiconductors such as diamond, Si, and SiC.