| Metadata | Details |
|---|
| Publication Date | 2020-06-29 |
| Journal | Nanophotonics |
| Authors | Bernard Gil, Guillaume Cassabois, R. CuscĂł, Giorgia Fugallo, LluĂs ArtĂșs |
| Institutions | Consejo Superior de Investigaciones CientĂficas, Centre National de la Recherche Scientifique |
| Citations | 50 |
| Analysis | Full AI Review Included |
- Deep Ultraviolet (DUV) Emitters: hBN is a leading material for DUV optoelectronics, achieving strong emission at 215 nm (5.75 eV). This wavelength is critical for sanitary applications (e.g., DNA/RNA absorption, virus killing).
- High Quantum Efficiency: Despite being an indirect band gap semiconductor in bulk form, hBN exhibits unusually strong exciton-phonon coupling, enabling efficient radiative recombination with an Internal Quantum Efficiency (IQE) up to 50% at room temperature.
- Ultra-High Thermal Conductivity: Isotopic purification (e.g., 10BN) boosts the in-plane thermal conductivity (kp) to a record 850 W/mK at 300 K, making hBN an excellent substrate for thermal management in high-power devices.
- Hyperbolic Nanophotonics: hBN supports hyperbolic phonon polaritons in the mid-infrared, specifically in two Reststrahlen bands (around 6 ”m and 12 ”m), enabling light squeezing and hyper-lensing effects.
- Quantum Emitters (SPS): Lattice defects within hBN act as robust Single Photon Sources (SPS) across a wide energy range (1.5 eV to 4 eV), positioning hBN as a strong contender against diamond NV centers for modern quantum technologies.
- Structural Anisotropy: The layered, AAâ stacking structure results in giant natural optical and thermal anisotropy, which is leveraged for both nanophotonics and thermal dissipation strategies.
| Parameter | Value | Unit | Context |
|---|
| Fundamental Band Gap (Bulk) | Indirect (M to K) | - | Bulk hBN crystals |
| Monolayer Band Gap | Direct (K point) | - | Monolayer hBN (MLBN) |
| Intrinsic Emission Wavelength | 215 | nm | Deep UV emission |
| Intrinsic Emission Energy | 5.75 | eV | Deep UV emission |
| Internal Quantum Efficiency (IQE) | 50 | % | Measured at room temperature (RT) |
| In-Plane Thermal Conductivity (kp) | 850 | W/mK | Record value for isotopically pure 10BN at 300 K |
| Out-of-Plane Thermal Conductivity (kz) | 10 | W/mK | For isotopically pure 10BN at 300 K |
| High-Frequency Raman Mode (E2ghigh) | 1369 | cm-1 | Measured at 77 K (in-plane vibration) |
| Low-Frequency Raman Mode (E2glow) | 52.7 | cm-1 | Measured at 77 K (interlayer gliding motion) |
| IR Reststrahlen Band 1 (Type I) | 784-819 | cm-1 | Corresponds to ~12 ”m wavelength |
| IR Reststrahlen Band 2 (Type II) | 1367-1607 | cm-1 | Corresponds to ~6 ”m wavelength |
| Indirect Exciton Energy (iX) | 5.955 | eV | Forbidden transition energy |
| SPS Emission Range (Defects) | 1.5 to 4 | eV | Broad range of single photon emitters |
| Melting Temperature | ~2950 | °C | High temperature stability |
| c-axis Lattice Parameter (AAâ stacking) | 0.666 | nm | Distance between adjacent B3N3 planes |
The research and development of hBN rely on advanced synthesis and characterization techniques:
- High-Temperature/High-Pressure Synthesis (HPHT): Used for growing large, high-quality bulk single crystals (e.g., 1 x 1 x 0.2 mm3 platelets). Growth is typically realized from a melt of precursors, often involving metal fluxes (e.g., Fe-Cr, Ba-BN).
- Epitaxial Growth Techniques:
- MOCVD (Metal Organic Chemical Vapor Deposition): Used for growing thin films and epilayers on substrates like sapphire.
- MBE (Molecular Beam Epitaxy): Used for high-quality, controlled growth of few-layer and monolayer hBN on substrates like copper (Cu) or Highly Ordered Pyrolytic Graphite (HOPG).
- Isotopic Engineering: Synthesis using mono-isotopically purified boron (10B or 11B) and nitrogen precursors to suppress mass fluctuations, thereby reducing phonon scattering and increasing thermal conductivity and phonon lifetime.
- Advanced Optical Spectroscopy:
- PL/CL (Photoluminescence/Cathodoluminescence): Used to study intrinsic exciton transitions (DUV) and defect-related emissions (SPS). CL imaging is crucial for spatially resolving localized defects.
- Raman and Infrared (IR) Spectroscopy: Essential for characterizing lattice vibrations, determining phonon dispersion, and measuring the dielectric constant components (Δxx and Δzz) that define the Reststrahlen bands.
- Theoretical Modeling (Ab Initio): Density Functional Theory (DFT) and calculations based on the Boltzmann Transport Equation (BTE) are used to predict thermal conductivity, phonon dispersion, and identify the atomic structure and optical properties of various lattice defects.
| Industry/Field | Specific Application/Product | Technical Advantage Leveraged |
|---|
| Deep UV Optoelectronics | DUV LEDs and Laser Diodes (200-300 nm range) | Ultra-short emission wavelength (215 nm), high IQE (50% RT), superior to AlN-based devices (limit ~235 nm). |
| Sanitary/Medical | Sterilization, water purification, air treatment, medical imaging | Efficient light absorption by nucleic acids (DNA/RNA) in the 200 nm range; effective killing of viruses (e.g., COVID-19) and bacteria. |
| Thermal Management | High-power electronic device substrates, heat spreaders | Record in-plane thermal conductivity (up to 850 W/mK) in isotopically pure crystals, crucial for miniaturized devices. |
| Quantum Technologies | Single Photon Sources (SPS), Quantum Information Processing | Robust, room-temperature operating defects (1.5 eV to 4 eV) that can challenge diamond NV centers and SiC double vacancies. |
| Nanophotonics/Imaging | Hyper-lensing, medical diagnosis, infrared light management | Hyperbolic phonon polaritons in the 6 ”m and 12 ”m bands, allowing light squeezing and manipulation of electromagnetic fields at sub-diffraction limits. |
| 2D Materials Technology | Passivation layers, release layers, dielectric barriers | Chemical inertness, high melting point, and easy cleavage property (van der Waals bonding) for fabricating complex heterostructures. |
| Nuclear/Security | Solid-state Neutron Detectors | High cross-section interaction of neutrons with 10B atoms, enhanced by using 10B mono-isotopically purified hBN. |
View Original Abstract
Abstract We review the recent progress regarding the physics and applications of boron nitride bulk crystals and its epitaxial layers in various fields. First, we highlight its importance from optoelectronics side, for simple devices operating in the deep ultraviolet, in view of sanitary applications. Emphasis will be directed towards the unusually strong efficiency of the exciton-phonon coupling in this indirect band gap semiconductor. Second, we shift towards nanophotonics, for the management of hyper-magnification and of medical imaging. Here, advantage is taken of the efficient coupling of the electromagnetic field with some of its phonons, those interacting with light at 12 and 6 ”m in vacuum. Third, we present the different defects that are currently studied for their propensity to behave as single photon emitters, in the perspective to help them becoming challengers of the NV centres in diamond or of the double vacancy in silicon carbide in the field of modern and developing quantum technologies.