Band offset between cubic boron nitride and nitrogen-plasma terminated boron-doped diamond (111)

At a Glance

Metadata	Details
Publication Date	2025-10-23
Journal	Applied Physics Letters
Authors	Ali Ebadi Yekta, Martha R. McCartney, David J. Smith, Norio Tokuda, R. J. Nemanich
Institutions	Arizona State University, Kanazawa University
Analysis	Full AI Review Included

Technical Documentation & Analysis: c-BN/BDD Heterostructures

Executive Summary

This research successfully demonstrates the fabrication and characterization of a cubic boron nitride (c-BN) dielectric layer epitaxially grown on nitrogen-plasma terminated boron-doped diamond (BDD) (111) substrates, confirming its viability for next-generation ultra-wide bandgap (UWBG) electronics.

Critical Band Alignment: Experimental measurement confirmed a Valence Band Offset (VBO) of +0.4 eV between c-BN and N-terminated diamond, resulting in a Type II staggered band alignment.
Electron Confinement: The resulting Conduction Band Offset (CBO) is calculated to be 1.3 eV, which is sufficient to confine electrons, validating c-BN as a superior gate dielectric for electron channel diamond Metal-Insulator-Semiconductor Field Effect Transistors (MISFETs).
Epitaxial Quality: Cross-sectional High-Resolution Transmission Electron Microscopy (XTEM) confirmed the excellent epitaxy of the c-BN layer on the (111)-oriented BDD substrate, crucial for high-performance device integration.
Material Requirement: The study relied on high-quality, precisely oriented (111) Boron-Doped Diamond (BDD) substrates, a core capability of 6CCVD’s MPCVD production line.
Methodology: The interface was engineered using nitrogen plasma termination (ECR-PECVD) prior to c-BN deposition via fluorine-based ECR-PECVD chemistry.
6CCVD Value Proposition: 6CCVD provides the necessary custom MPCVD BDD substrates (SCD and PCD) with precise orientation control, doping levels, and surface preparation expertise required to replicate and scale this advanced heterostructure technology.

Technical Specifications

Hard data extracted from the research paper detailing material properties and experimental results.

Parameter	Value	Unit	Context
Valence Band Offset (VBO)	+0.4	eV	c-BN VBM relative to N-Diamond VBM
Conduction Band Offset (CBO)	1.3	eV	Calculated based on E_g (5.5 eV & 6.4 eV)
Diamond Bandgap (E_g)	5.5	eV	UWBG material
c-BN Bandgap (E_g)	6.4	eV	UWBG material
Substrate Material	HPHT Monocrystalline Type IIb BDD	N/A	(111) orientation
Substrate Dimensions	3 x 3 x 0.3	mm³	Sample size used for characterization
Boron Concentration Target	250	ppm	Substrate doping level
Substrate Orientation Miscut	±1.5	°	(111) surface tolerance
RMS Roughness (AFM)	~0.7	nm	Required surface quality for epitaxy
Nitrogen Surface Coverage (σ_N)	2.54 x 10¹⁵	atoms/cm²	Achieved after N-plasma termination
Projected Breakdown Field (Diamond/c-BN)	≥ 10	MV/cm	Crucial characteristic for high-power devices

Key Methodologies

A concise, ordered list detailing the critical processing steps used to achieve the c-BN/N-BDD (111) interface.

Substrate Cleaning:
- Boiling acid mixture (H₂SO₄/H₂O₂/H₂O, 3:1:1) at 220 °C for 15 min.
- HF treatment for 10 min.
- Boiling solution (NH₄OH/H₂O₂/H₂O, 1:1:5) at 75 °C for 15 min.
Hydrogen Plasma Cleaning (ECR-PECVD):
- Purpose: Surface cleaning prior to termination.
- Recipe: H₂ flow (10 sccm), Pressure (2 x 10^-5 Torr), MW Power (0.3 kW), Temperature (650 °C).
Nitrogen Plasma Termination (ECR-PECVD):
- Purpose: Establish C-N bonding at the diamond surface.
- Recipe: N₂ flow (50 sccm), Pressure (9.6 x 10^-5 Torr), MW Power (0.6 kW), Duration (30 min).
c-BN Epitaxial Growth (ECR-PECVD, Fluorine Chemistry):
- Purpose: Deposit high-quality c-BN dielectric layer.
- Precursors: H₂, BF₃, N₂, He, Ar (Flow rates: 4, 4, 25, 70, 5 sccm, respectively).
- Pressure: 1.4 x 10^-4 Torr.
- MW Power: 1.4 kW.
- Substrate Temperature: 850 °C.
- Substrate DC Bias: -40 V.
Characterization: In situ X-ray Photoemission Spectroscopy (XPS) and Ultraviolet Photoemission Spectroscopy (UPS) were used to determine core level binding energies and Valence Band Maxima (VBM), followed by Cross-sectional Transmission Electron Microscopy (XTEM) for epitaxy confirmation.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials necessary to replicate and scale this critical research into high-power diamond MISFETs. Our MPCVD capabilities exceed the specifications of the HPHT substrates used in this study, offering superior scalability and purity.

Applicable Materials

To replicate or extend this research, high-quality, precisely doped and oriented diamond substrates are essential. 6CCVD recommends the following materials:

6CCVD Material Solution	Specification & Relevance to Research
Heavy Boron Doped SCD (111)	Direct replacement for the BDD substrate used. We offer precise, uniform boron doping (BDD) up to 500 µm thick, ensuring consistent electrical properties for electron channel devices.
Optical Grade SCD (111)	For studies requiring ultra-low defect density or alternative doping schemes (e.g., nitrogen incorporation for NV centers, if extending the research). Polishing available to Ra < 1 nm.
Large-Area BDD PCD	For scaling up device fabrication. We offer Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, doped with boron, providing a cost-effective platform for industrial prototyping.

Customization Potential

The success of the c-BN/BDD heterostructure relies on precise material engineering. 6CCVD offers comprehensive customization services to meet the exact needs of UWBG device development:

Custom Dimensions and Thickness: While the paper used 3 x 3 x 0.3 mm³ samples, 6CCVD can supply SCD wafers up to 15 x 15 mm and PCD wafers up to 125 mm in custom thicknesses (0.1 µm to 500 µm).
Orientation Control: We guarantee precise (111) orientation control, critical for achieving the reported band alignment and epitaxial quality.
Surface Preparation: We provide ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD) necessary for subsequent plasma termination and epitaxial growth processes.
Integrated Metalization: For completing MISFET structures, 6CCVD offers in-house deposition of custom contact layers, including Au, Pt, Pd, Ti, W, and Cu, tailored to specific device architectures.

Engineering Support

The measurement of the VBO and CBO is fundamental to designing functional diamond MISFETs. 6CCVD’s in-house PhD material science team specializes in UWBG heterostructures and can provide expert consultation on:

Material Selection: Optimizing BDD doping concentration and substrate thickness for specific electron channel diamond MISFET projects.
Interface Engineering: Advising on the impact of surface termination (e.g., N-plasma vs. O-plasma) on band alignment and device performance.
Scaling and Integration: Assisting engineers in transitioning from small-scale research samples to large-area, production-ready diamond wafers.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to ensure rapid delivery of your critical diamond materials.

View Original Abstract

Diamond electronics has attracted attention for high power and high frequency device applications. Cubic boron nitride (c-BN) may be considered as a suitable dielectric layer for electron channel diamond metal-insulator-semiconductor field effect transistors (MISFETs) provided that its valence band edge can be positioned above that of diamond. This study reports experimental measurement of the valence band offset (VBO) between c-BN and nitrogen-plasma terminated boron-doped diamond (111). Nitrogen plasma processing was used to produce C-N bonding at the diamond surface. Electron cyclotron resonance plasma enhanced chemical vapor deposition was then used to deposit epitaxial c-BN films on the N-terminated diamond substrate, as confirmed by cross-sectional high-resolution electron microscopy. X-ray and ultraviolet photoemission spectroscopies indicated that the valence band maximum of c-BN is positioned 0.4 eV above that of diamond resulting in a type II staggered band alignment. This result is consistent with theoretical predictions of the VBO between the two materials in the (111) surface orientation, indicating that c-BN with C-N interface bonding can be used as a dielectric layer for electron channel diamond (111) MISFET devices.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0278816

References

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2017 - Band offsets of epitaxial cubic boron nitride deposited on polycrystalline diamond via plasma-enhanced chemical vapor deposition [Crossref]
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1976 - Solid State Physics
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2024 - Face-centered cubic carbon as a fourth basic carbon allotrope with properties of intrinsic semiconductors and ultra-wide bandgap [Crossref]
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