Identification of the Nitrogen Interstitial as Origin of the 3.1 eV Photoluminescence Band in Hexagonal Boron Nitride
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-05-06 |
| Journal | physica status solidi (b) |
| Authors | Elham Khorasani, Thomas Frauenheim, Balint Aradi, Peter Deak, Elham Khorasani |
| Institutions | University of Bremen, Shenzhen Institute of Information Technology |
| Citations | 7 |
| Analysis | Full AI Review Included |
Technical Analysis & Documentation: Defect Engineering in Wide-Bandgap Materials
Section titled “Technical Analysis & Documentation: Defect Engineering in Wide-Bandgap Materials”This document analyzes the research paper “Identification of the Nitrogen Interstitial as Origin of the 3.1 eV Photoluminescence Band in Hexagonal Boron Nitride” and connects its findings on defect engineering in wide-bandgap semiconductors to 6CCVD’s advanced MPCVD diamond capabilities.
Executive Summary
Section titled “Executive Summary”This computational study provides critical insights into intrinsic defect behavior in hexagonal Boron Nitride (hBN), a material analogous to diamond in its application potential for quantum photonics and electronics.
- Defect Identification: The Nitrogen Interstitial ($N_i$) is identified as the intrinsic defect responsible for the experimentally observed 3.1 eV photoluminescence (PL) band in hBN.
- Computational Validation: Optimized screened hybrid functional (HSE) calculations were used, demonstrating high accuracy in predicting defect properties in wide-bandgap materials.
- Stability and Compensation: $N_i$ exhibits the lowest formation energy under N-rich, n-type conditions, confirming its role as a highly efficient compensating center.
- PL Energy Match: The calculated PL energy for $N_i$ (3.0 eV) shows excellent agreement with the experimentally measured N-sensitive band (3.1 eV).
- Vacancy Exclusion: The Nitrogen Vacancy ($V_N$) is definitively ruled out as the origin of the Three Boron Center (TBC) electron paramagnetic resonance (EPR) signal, as its calculated hyperfine coupling constant ($A_{ave} = 34.23$ MHz) is significantly lower than the experimental value (117.06 MHz).
- Market Relevance: This work underscores the necessity of precise defect control and ultra-pure substrates—core requirements for quantum material research, directly aligning with 6CCVD’s expertise in high-purity Single Crystal Diamond (SCD) for NV, SiV, and GeV center engineering.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the computational methodology and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Calculated PL Energy ($N_i$) | 3.0 | eV | Predicted energy of the N-related emission band. |
| Experimental PL Band | 3.1 | eV | Previously observed N-sensitive band in hBN. |
| Hybrid Functional Mixing ($\alpha$) | 0.3 | - | Optimized parameter for HSE functional in bulk hBN. |
| Hybrid Functional Screening ($\mu$) | 0.4 | - | Optimized parameter for HSE functional in bulk hBN. |
| Wave Function Cutoff | 420 (840) | eV | Energy cutoff applied for wave function expansion. |
| Geometry Relaxation Force Criterion | 0.01 | eV/Å | Convergence threshold for defect geometry optimization. |
| $N_i$ Adiabatic Transition Level $E(+/0)$ | 0.94 | eV | Relative to Valence Band Maximum (VBM). |
| $N_i$ Adiabatic Transition Level $E(0/-)$ | 2.68 | eV | Relative to Valence Band Maximum (VBM). |
| High-Frequency Dielectric Constant ($\epsilon_{\infty}$) | 4.10 | - | Used for charged defect correction (SLABCC). |
| Calculated $V_N$ Average Hyperfine Coupling ($A_{ave}$) | 34.23 | MHz | Calculated value for the $V_N$ defect model. |
| Experimental TBC Average Hyperfine Coupling ($A_{ave}$) | 117.06 | MHz | Measured value for the Three Boron Center (TBC). |
| $N_i$-N Bondlength | 1.38 | Å | Calculated bond length in the lowest energy $N_i$ configuration. |
Key Methodologies
Section titled “Key Methodologies”The study relied on advanced first-principles calculations to model defect stability and optical properties in hBN.
- Computational Platform: Calculations were performed using the Vienna Ab initio Simulation Package (VASP 5.4.4) employing the Projector Augmented Wave (PAW) method.
- Functional Selection: An optimized screened hybrid functional (HSE($\alpha, \mu$)) was utilized, specifically tuned with a mixing parameter $\alpha = 0.3$ and a screening parameter $\mu = 0.4$ to accurately reproduce the hBN band gap and satisfy the generalized Koopmans condition.
- Supercell and Geometry: Bulk hBN was modeled using an orthogonal supercell containing 120 atoms. Defect geometries were relaxed at fixed lattice constants using a strict force criterion of 0.01 eV/Å.
- Interlayer Interaction: Van der Waals (vdW) interactions were included using the Tkatchenko-Scheffler method ($s_R = 0.96$).
- Charged Defect Correction: Total energies for charged defects were corrected a posteriori using the SLABCC code, applying the high-frequency dielectric constant ($\epsilon_{\infty} = 4.10$) to eliminate artificial interactions between periodic charges.
- PL Energy Calculation: Photoluminescence was simulated as a donor-acceptor recombination (bound exciton). The PL energy was calculated as the difference between the total energy of the initial state (electron in the Conduction Band Minimum, CBM) and the final state (relaxed geometry after recombination).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The rigorous defect analysis performed in this research highlights the critical need for materials with controlled purity and precise defect engineering—a core competency of 6CCVD in the MPCVD diamond sector. Our capabilities are perfectly suited to support researchers working on analogous quantum defect systems (e.g., NV, SiV, GeV centers) in diamond.
| Research Requirement/Challenge | 6CCVD Solution & Capability |
|---|---|
| Need for Ultra-High Purity Substrates | Optical Grade Single Crystal Diamond (SCD): To isolate and study specific quantum defects (like $N_i$ in hBN or NV centers in diamond), background impurities must be minimized. 6CCVD supplies high-purity SCD grown via MPCVD, ensuring minimal native nitrogen (P1 centers) and superior optical clarity. |
| Precise Defect Control (e.g., $N_i$ incorporation) | Custom Doping and Growth Recipes: We offer SCD and Polycrystalline Diamond (PCD) with controlled doping levels. This includes low-concentration nitrogen incorporation for NV center creation or heavy Boron-Doped Diamond (BDD) for electrochemical and conductive applications. |
| Integration into Quantum Devices (PL/EPR) | Advanced Metalization Services: Device integration requires robust electrical contacts and thermal management layers. 6CCVD provides in-house metalization capabilities, including deposition of Ti/Pt/Au, W, Pd, and Cu stacks, tailored to specific device architectures. |
| Surface Quality for Optical Interfaces | Precision Polishing (Ra < 1 nm): For high-fidelity PL and quantum sensing applications, surface roughness must be minimal. Our SCD wafers are polished to achieve a surface roughness (Ra) < 1 nm, crucial for reducing scattering and improving coupling efficiency. |
| Custom Dimensions and Thickness | Flexible Manufacturing: We provide custom dimensions for both SCD (0.1 µm - 500 µm thickness) and large-area PCD plates (up to 125 mm diameter, 0.1 µm - 500 µm thickness). Substrates up to 10 mm thick are also available. |
| Engineering Support for Material Selection | In-House PhD Expertise: Our team of material scientists specializes in correlating MPCVD growth parameters with resulting electronic and optical properties. We offer consultation to optimize material selection for quantum computing, sensing, and high-power electronics projects. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).
View Original Abstract
Nitrogen interstitials () have the lowest formation energy among intrinsic defects of hexagonal boron nitride (hBN) under n‐type and N‐rich conditions. Using an optimized hybrid functional, which reproduces the gap and satisfies the generalized Koopman’s condition, an configuration is found, which is lower in energy than the ones reported so far. The (0/-) charge transition level is also much deeper, so acts as a very efficient compensating center in n‐type samples. Its calculated photoluminescence (PL) at 3.0 eV agrees well with the position of an N‐sensitive band measured at 3.1 eV. It is also found that the nitrogen vacancy () cannot be the origin of the three‐boron‐center (TBC) electron paramagnetic resonance (EPR) center and in thermal equilibrium it is even unlikely to exist in n‐type samples.