Orientation Dependence of Cathodoluminescence and Photoluminescence Spectroscopy of Defects in Chemical-Vapor-Deposited Diamond Microcrystal

At a Glance

Metadata	Details
Publication Date	2020-11-29
Journal	Materials
Authors	K. Fabisiak, Szymon Łoś, K. Paprocki, Mirosław Szybowicz, Janusz Winiecki
Institutions	Nicolaus Copernicus University, Institute of Physics
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Analysis: Defect Engineering in CVD Diamond

Reference Paper: Orientation Dependence of Cathodoluminescence and Photoluminescence Spectroscopy of Defects in Chemical-Vapor-Deposited Diamond Microcrystal (Materials 2020, 13, 5446)

Executive Summary

This research highlights the critical dependence of diamond crystal quality and defect concentration on crystallographic orientation, providing key insights for quantum and optoelectronic applications.

Orientation Dependence: The study confirms that (111) crystallographic planes exhibit significantly higher structural defect concentrations (dislocations, stacking faults) compared to (100) planes.
Quantified Defect Density: Estimated defect concentration for (111) planes (3.5 x 10¹⁸ cm^-3) was found to be nearly an order of magnitude higher than for (100) planes (8.3 x 10¹⁷ cm^-3).
Structural Defect Signature: Lattice disorder, specifically dislocations, was directly correlated with the blue-violet A-band emission observed in Cathodoluminescence (CL) spectra at 2.815 eV.
Raman Quality Metric: Raman Full Width at Half Maximum (FWHM) serves as a robust measure of crystal quality. The Element Six (100) SCD reference crystal (4.7 cm^-1) demonstrated superior quality compared to the HF CVD grown (100) (8.6 cm^-1) and (111) (13.7 cm^-1) microcrystals.
Quantum Center Identification: Key nitrogen-vacancy (NV) centers were identified, including the neutral NV⁰ (2.156 eV) and the negatively charged NV^- (1.947 eV), crucial for quantum computing and sensing applications.
Stress Analysis: The HF CVD microcrystals were found to be under significant compressive stress, estimated at approximately 3 GPa.

Technical Specifications

The following hard data points were extracted from the analysis of the HF CVD diamond microcrystals and reference material:

Parameter	Value	Unit	Context
Raman FWHM (Element Six SCD)	4.7	cm^-1	Benchmark (100) Monocrystal Quality
Raman FWHM (HF CVD)	8.6	cm^-1	(100) Microcrystal Quality
Raman FWHM (HF CVD)	13.7	cm^-1	(111) Microcrystal Quality (Highest Defect)
Estimated Defect Concentration (111)	3.5 x 10¹⁸	cm^-3	Calculated from FWHM (L^-3 relation)
Estimated Defect Concentration (100)	8.3 x 10¹⁷	cm^-3	Calculated from FWHM (L^-3 relation)
Internal Stress (Compressive)	~3	GPa	Indicated by Raman peak shift
A-Band Emission Peak	2.815	eV	Associated with lattice dislocations (CL)
Neutral NV Center (NV⁰)	2.156	eV	Observed in CL/PL spectra
Negative NV Center (NV^-)	1.947	eV	Observed in PL spectra (Potential Qubit)
GR1 Defect (V⁰)	1.675	eV	Observed in PL spectra (Vacancy in neutral state)
Substrate Temperature (Growth)	1000	K	HF CVD Process Parameter
Filament Temperature (Growth)	2100	°C	HF CVD Process Parameter
Total Pressure (Growth)	80	mbar	HF CVD Process Parameter

Key Methodologies

The investigation utilized a combination of synthesis and advanced spectroscopic techniques to characterize defect types and structural quality.

Synthesis Method: Diamond microcrystals were grown using Hot-Filament Chemical Vapor Deposition (HF CVD) on (100) oriented silicon substrates.
Growth Recipe: The process utilized a methane/hydrogen gas mixture (CH₄ / H₂ = 1 vol.%) at a total pressure of 80 mbar. The substrate temperature was maintained at 1000 K.
Activation Source: A tungsten filament, heated to 2100 °C, was used for thermal activation of the gas mixture.
Morphological Analysis: Scanning Electron Microscopy (SEM) operating at 20 kV was used to examine crystal morphology and grain sizes (up to 20 µm).
Defect Spectroscopy (CL): Cathodoluminescence (CL) spectra were registered at room temperature using a 30 kV electron beam, providing high-resolution analysis of color centers in the 190-1100 nm range.
Defect Spectroscopy (PL/RS): Confocal micro Raman Spectroscopy (RS) and Photoluminescence (PL) were performed using a 488 nm Argon laser (1 mW power) in backscattering geometry, with a spatial resolution of 1 µm.

6CCVD Solutions & Capabilities

The research demonstrates that high-quality, low-defect diamond material, particularly with (100) orientation, is essential for advanced applications like quantum sensing and optoelectronics. The limitations observed in the HF CVD material (high FWHM, high defect concentration, significant compressive stress) are directly addressed by 6CCVD’s advanced Microwave Plasma CVD (MPCVD) capabilities.

Applicable Materials for Replication and Extension

To replicate or extend this research—especially for achieving stable, high-coherence NV centers—researchers require diamond with minimal lattice disorder and precise orientation control.

6CCVD Material Recommendation	Rationale & Advantage over HF CVD
High-Purity Optical Grade SCD (100)	Essential for minimizing structural defects (dislocations, stacking faults) which compete with NV center luminescence (A-band emission). 6CCVD’s MPCVD process yields significantly lower FWHM values than the 4.7 cm^-1 benchmark, ensuring superior crystal quality and reduced internal stress.
Nitrogen-Doped SCD (Controlled N)	For intentional creation of NV centers. 6CCVD offers precise gas control during MPCVD growth to tune nitrogen incorporation, optimizing the ratio of NV^- (qubit) to NV⁰ centers.
Boron-Doped Diamond (BDD)	The paper’s introduction mentions BDD for semiconductor devices. 6CCVD provides heavily or lightly doped BDD films (SCD or PCD) for electrochemical or electronic applications.

Customization Potential for Advanced Device Integration

The transition from microcrystals to functional devices requires precise engineering not achievable with standard HF CVD growth. 6CCVD provides the necessary customization:

Large-Area, Low-Defect Substrates: While the paper studied 20 µm microcrystals, 6CCVD supplies Single Crystal Diamond (SCD) plates up to 500 µm thick and Polycrystalline Diamond (PCD) wafers up to 125mm in diameter, enabling scalable device fabrication.
Superior Surface Finish: The high defect density in the HF CVD material complicates surface preparation. 6CCVD guarantees ultra-smooth polishing: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, critical for minimizing surface scattering losses in optical applications.
Custom Metalization Schemes: If the research progresses to fabricating electrodes or contacts for electrical characterization (e.g., measuring charge state conversion of NV centers), 6CCVD offers in-house deposition of standard and custom metal stacks, including Ti, Pt, Au, Pd, W, and Cu.
Precise Thickness Control: 6CCVD offers SCD and PCD layers with thickness control from 0.1 µm up to 500 µm, allowing engineers to optimize layer depth for specific defect implantation or surface-sensitive experiments.

Engineering Support

The high compressive stress (3 GPa) and high FWHM observed in the HF CVD material are significant barriers to high-performance quantum and electronic devices.

Stress Mitigation: 6CCVD’s in-house PhD team specializes in optimizing MPCVD growth parameters to minimize internal strain and achieve low-stress diamond films, directly addressing the limitations found in this study.
Material Selection for Quantum Projects: Our experts provide consultation on material selection (e.g., high-purity SCD vs. low-stress PCD) and orientation preference (confirming the superiority of (100) growth) for similar NV Center Quantum Sensing projects.
Global Logistics: 6CCVD ensures reliable, global shipping (DDU default, DDP available) for sensitive diamond materials, supporting international research efforts.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Point defects, impurities, and defect-impurity complexes in diamond microcrystals were studied with the cathodoluminescence (CL) spectroscopy in the scanning electron microscope, photoluminescence (PL), and Raman spectroscopy (RS). Such defects can influence the directions that microcrystals are grown. Micro-diamonds were obtained by a hot-filament chemical vapor deposition (HF CVD) technique from the methane-hydrogen gas mixture. The CL spectra of diamond microcrystals taken from (100) and (111) crystallographic planes were compared to the CL spectrum of a (100) oriented Element Six diamond monocrystal. The following color centers were identified: 2.52, 2.156, 2.055 eV attributed to a nitrogen-vacancy complex and a violet-emitting center (A-band) observed at 2.82 eV associated with dislocation line defects, whose atomic structure is still under discussion. The Raman studies showed that the planes (111) are more defective in comparison to (100) planes. What is reflected in the CL spectra as (111) shows a strong band in the UV region (2.815 eV) which is not observed in the case of the (100) plane.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13235446

References

2002 - Development of diamond-coated drills and their cutting performance [Crossref]
2002 - Application of diamond coatings onto small dental tools [Crossref]
2018 - Recent advances in diamond power semiconductor devices [Crossref]
2016 - Diamond particle detectors for high energy physics [Crossref]
2016 - Highly efficient and stable ultraviolet photocathode based on nanodiamond particles [Crossref]
2017 - UV photocathodes based on nanodiamond particles: Effect of carbon hybridization on the efficiency [Crossref]
2000 - The Physical Implementation of Quantum Computation [Crossref]
2020 - Morphological, cathodoluminescence and thermoluminescence studies of defects in diamond films grown by HF CVD technique [Crossref]
2016 - A Raman spectroscopy study of the effect of thermal treatment on structural and photoluminescence properties of CVD diamond films [Crossref]
2013 - Influence of boron on donor-acceptor pair recombination in type IIa HPHT diamonds [Crossref]