Enhanced Lateral Growth of Homoepitaxial (001) Diamond by Microwave Plasma Chemical Vapor Deposition with Nitrogen Addition

At a Glance

Metadata	Details
Publication Date	2025-10-30
Journal	Coatings
Authors	Tzu-I Yang, Chia-Yen Chuang, Junbin Huang, Cheng‐Jung Ko, Wei-Lin Wang
Institutions	National Chung Shan Institute of Science and Technology, National Yang Ming Chiao Tung University
Analysis	Full AI Review Included

Executive Summary

This study successfully demonstrates an enhanced, high-rate lateral growth strategy for homoepitaxial (001) single-crystal diamond (SCD) using Microwave Plasma Chemical Vapor Deposition (MPCVD) assisted by nitrogen (N₂) addition.

Optimal Lateral Growth: A nitrogen concentration of 180 ppm yielded the maximum lateral expansion without significant polycrystalline diamond (PCD) rim formation.
Substantial Area Gain: The SCD top surface area increased by a factor of 1.6 relative to the initial substrate area (5.5 mm to 7.6 mm edge length) after only 20 hours of growth.
Balanced High Growth Rates: The lateral growth rate (GR[100]) reached 52.5 µm/h, closely matching the vertical growth rate (GR[001]) of 47.3 µm/h, resulting in a favorable growth ratio (lambda) near 1.1.
Improved Crystalline Quality: The laterally expanded regions exhibited a threading dislocation density (EPD) of ~6.7 x 10⁴ cm^-2, approximately one order of magnitude lower than the central region (~6.0 x 10⁵ cm^-2).
Structural Integrity: Raman and AFM analyses confirmed uniform crystalline quality and low residual stress across the entire expanded top surface and the grown side face.
High Purity Verification: High-Resolution X-ray Diffraction (HRXRD) showed a narrow Full Width at Half Maximum (FWHM) of 11 arcsec for the (004) reflection, confirming high crystallinity.

Technical Specifications

Parameter	Value	Unit	Context
Optimal N₂ Concentration	180	ppm	Maximizing lateral growth (N180 sample)
Vertical Growth Rate (GR[001])	47.3	µm/h	N180 sample
Lateral Growth Rate (GR[100])	52.5	µm/h	N180 sample (excluding PCD)
Growth Rate Ratio (lambda)	1.1	N/A	GR[100] / GR[001] for N180
Total Growth Duration	20	h	N180 sample
Final Edge Length	7.6	mm	Expanded SCD (Initial: 5.5 mm)
Lateral Area Gain	1.6	N/A	Relative increase in top surface area
Final Thickness	0.95	mm	N180 sample
XRC FWHM (004)	11	arcsec	Grown diamond layer (High crystallinity)
Raman FWHM (Center)	2.8	cm^-1	Diamond peak at ~1332 cm^-1
EPD (Lateral Region)	~6.7 x 10⁴	cm^-2	Dislocation density in expanded area
EPD (Central Region)	~6.0 x 10⁵	cm^-2	Dislocation density over original substrate

Key Methodologies

The homoepitaxial growth of (001) SCD was performed using a 6 kW / 2.45 GHz ASTeX-type MPCVD system under high-rate growth conditions.

1. Substrate Preparation

Substrate: Polished (001)-oriented synthetic CVD diamond (5.5 x 5.5 x 0.5 mm³) with a miscut angle of less than or equal to 1°.
Cleaning: Ultrasonic cleaning in acetone and ethanol (10 min each).
Acid Treatment (Two-Step):
1. H₂O₂:H₂SO₄ (1:4 ratio) at 200 °C for 0.5 h.
2. HNO₃:H₂SO₄ (1:4 ratio) at 300 °C for 0.5 h (to remove sp² carbon).
Pre-treatment: Hydrogen plasma treatment at 5000 W and 1.67 x 10⁴ Pa (125 Torr) for 20 min to remove surface residues.

2. MPCVD Growth Parameters (N180 Optimal Condition)

Parameter	Value	Unit	Notes
Microwave Power	5600	W	High power density regime
Source Gas Mixture	10% CH₄-H₂	N/A	High methane concentration
N₂ Concentration	180	ppm	Optimal concentration for lateral growth
Total Gas Flow Rate	500	sccm	N/A
Pressure	1.87 x 10⁴ Pa (140 Torr)	Pa (Torr)	Elevated pressure
Substrate Temperature	1180	°C	Measured via 2-color thermo-pyrometer
Growth Duration	20	h	N/A

3. Characterization Techniques

Crystalline Quality: High-Resolution X-ray Diffraction (HRXRD) using symmetric (004) and asymmetric (113) reflections (2θ-ω scans and rocking curves).
Structural Uniformity: Raman spectroscopy (488 nm laser) to measure Raman shift and FWHM across the top and side faces.
Surface Morphology: Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM).
Defect Analysis: Photoluminescence (PL) spectroscopy (488 nm excitation) to analyze Nitrogen-Vacancy (NV⁰ and NV^-) centers.
Dislocation Density: Etch Pit Density (EPD) analysis performed after H₂/O₂ plasma etching (4.0 kW, 100 Torr, 3% O₂, 0.25 h) to reveal threading dislocations.

Commercial Applications

The ability to synthesize large-area, high-quality SCD with significantly reduced dislocation density in the expanded regions is critical for next-generation diamond-based technologies.

Application Area	Relevance of Enhanced Lateral Growth
High-Power Integrated Electronics	Large, low-defect substrates are essential for high-voltage, high-frequency devices (e.g., Schottky diodes, FETs) that exploit diamond’s high breakdown field and thermal conductivity.
Quantum Information Processing	SCD is the leading platform for solid-state qubits based on NV centers. Larger, high-purity substrates with low background defects improve qubit yield and coherence times.
Ultraviolet (UV) and Radiation Detection	Large-area, uniform SCD films are required for high-sensitivity detectors used in harsh environments or specialized scientific instruments.
Fusion Windows and Optics	Diamond’s ultra-wide bandgap and high thermal stability make it ideal for optical windows in high-energy systems; large, high-quality crystals minimize scattering and absorption losses.
Thermal Management	Large SCD plates are used as heat spreaders in high-density electronic packages (e.g., RF modules), requiring the material to be uniform and scalable.
Mechanical Machining/Tools	Scalable, high-quality SCD growth reduces the cost of producing diamond cutting tools and wear-resistant components.

View Original Abstract

Diamond, as an exceptional material with many superior properties, requires a single crystal in a reasonably large size for practical industrial applications. However, achieving large-area single-crystal diamond (SCD) growth without the formation of polycrystalline rims remains challenging. Microwave plasma chemical vapor deposition (MPCVD) using a gas mixture of 10% CH4-H2 was used for the homoepitaxial growth of (001) SCD. The effect of nitrogen gas addition in the range of 0-2000 ppm on lateral growth was investigated. Deposition with 180 ppm N2 over a growth duration of 20 h to reach a thickness of 0.95 mm resulted in significantly enhanced lateral growth without the appearance of a polycrystalline diamond (PCD) rim for the grown diamond, and the total top surface area of SCD increased by an area gain of 1.6 relative to the substrate. The corresponding vertical and lateral growth rates were 47.3 µm/h and 52.5 µm/h, respectively. Characterization by Raman spectroscopy and atomic force microscopy (AFM) revealed uniform structural integrity across the whole surface from the laterally grown regions to the center, including the entire expanded area, in terms of surface morphology and crystalline quality. Moreover, measurements of the etch pit densities (EPDs) showed a substantial reduction in the laterally grown regions, approximately an order of magnitude lower than those in the central region. The high quality of the homoepitaxial diamond layer was further verified with (004) X-ray rocking curve analysis, showing a narrow full width at half maximum (FWHM) of 11 arcsec.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15111256

References

2019 - Diamond power devices: State of the art, modelling, figures of merit and future perspective [Crossref]
2024 - Applications of diamond films: A review [Crossref]
2025 - Optical-grade diamond: Characteristics, synthesis, and recent research progress [Crossref]
2004 - Application of diamond in high technology [Crossref]
2012 - Homoepitaxial growth of single crystal diamond membranes for quantum information processing [Crossref]
2020 - Large-scale integration of artificial atoms in hybrid photonic circuits [Crossref]
2021 - Polishing and planarization of single crystal diamonds: State-of-the-art and perspectives [Crossref]
2013 - Diamond polishing [Crossref]
2023 - CVD diamond: A review on options and reality [Crossref]