Studies of Dislocations in Type Ib, Type IIa HPHT and CVD Single Crystal Diamonds

At a Glance

Metadata	Details
Publication Date	2023-04-11
Journal	Crystals
Authors	D.S. Misra
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: Defect Control in Single Crystal Diamond

This documentation analyzes the findings regarding crystalline defects in Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) materials, focusing on the critical role of dislocation control for advanced electronic and optical applications.

Executive Summary

The reviewed research confirms that crystalline perfection, quantified by X-ray topography (XRT) and rocking curve FWHM, is the primary limiting factor for high-performance diamond applications.

Defect Impact: Dislocations, dislocation bundles, and aggregates severely degrade key SCD characteristics, including reducing breakdown voltage in high-power diodes, lowering charge collection efficiency (CCE) in detectors, and increasing birefringence in laser optics (requirement: < 10^-4).
HPHT Benchmark: High-Purity, Type IIa HPHT SCDs demonstrate the highest crystalline quality, achieving FWHM values near the theoretical limit (approx. 1 arc sec) and serving as the gold standard for defect-free material.
CVD Challenges: MPCVD-grown SCDs typically exhibit a much higher density of complex defects, including large dislocation aggregates (tens to hundreds of µm in size), which primarily originate from the substrate/film interface.
Strain Limitation: High internal strain, measured by rocking curve shift (θ), renders many CVD plates unsuitable for high-precision X-ray optics (e.g., monochromators), requiring curvature radii greater than 30 m.
Path to Perfection: Eliminating defects in CVD SCDs requires the use of ultra-low-defect substrates (e.g., Type IIa HPHT seeds) and detailed optimization of MPCVD growth parameters to prevent dislocation multiplication during epitaxial growth.
6CCVD Value Proposition: 6CCVD specializes in providing the necessary high-purity SCD substrates and large-area PCD materials, coupled with expert engineering support, to meet the stringent defect control requirements of next-generation diamond devices.

Technical Specifications

The following hard data points summarize the crystalline quality and defect requirements discussed in the review.

Parameter	Value	Unit	Context
HPHT Type IIa FWHM (Benchmark)	~1	arc sec	Achieved by defect-free, high-quality SCD.
HPHT Type Ib FWHM Range	4 to 8	arc sec	Typical range for Type Ib material (220 plane).
CVD SCD FWHM Range (High Defect)	10 to 40	arc sec	Observed in samples used for particle detectors.
Nitrogen Impurity (Type IIa HPHT)	Sub-parts per billion	ppb	Required for high-purity, low-defect growth.
Nitrogen Impurity (Type Ib HPHT)	Tens to Hundreds	ppm	Associated with line dislocations along <111> directions.
Optical Birefringence Requirement	< 10^-4	N/A	Critical for high-power laser window applications.
Unsuitable Curvature Radius (CVD)	< 10	m	Plates with high strain, unsuitable for X-ray monochromators.
XRT Angular Resolution (Synchrotron)	2	µm	Precision of defect mapping methodology.
Dislocation Aggregate Size (CVD)	Tens to Hundreds	µm	Size of defect clusters observed in CVD SCDs.

Key Methodologies

The research relies heavily on advanced X-ray characterization techniques to map and quantify crystalline defects.

Diamond Synthesis:
- MPCVD Growth: Utilizes Methane (CH₄) and Hydrogen (H₂) gases (typically > 6N purity) for epitaxial growth of SCDs, often on Type Ib HPHT substrates.
- HPHT Synthesis: Employs metal catalysts (Fe, Ni, Co) and small seed crystals (0.1-0.2 mm) to grow Type Ib and Type IIa SCDs.
- Isotopic Control: Growth recipes utilize controlled mixtures of ¹³CH₄ and ¹²CH₄ to study the impact of ¹³C content on thermal and structural properties.
Defect Characterization (XRT Techniques):
- Rocking Curve Mapping (RCM): Measures the FWHM of the Bragg peak for specific crystallographic planes ((111), (220), (400)) across the entire sample area using a monochromatic X-ray beam (e.g., 15 keV). FWHM values directly correlate with dislocation density and strain.
- XRT Imaging (Monochromatic): Captures images at a specific Bragg angle to visualize dislocations (dark lines/spots), dislocation bundles, and stacking faults (dark bands) against a grey background.
- White-Beam XRT Imaging: Illuminates the sample perpendicular to the beam incidence to generate images containing defect contrast, often used for rapid visualization, though resolution may be lower than RCM.
Strain and Curvature Analysis:
- RCM is used to track the shift in the Bragg angle (θ) across the sample plate, allowing for precise calculation of crystal curvature and internal strain, which is critical for X-ray optics suitability.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality diamond materials and customization services required to overcome the defect limitations identified in this research, enabling the successful fabrication of advanced diamond devices.

Applicable Materials for Defect Control

To replicate or extend the research findings, 6CCVD recommends materials optimized for low-defect epitaxial growth and high-performance applications:

Material Grade	Description	Application Focus	6CCVD Capability
Optical Grade SCD	Ultra-high purity, low-nitrogen SCD (Type IIa equivalent). Essential for use as defect-free substrates for subsequent CVD growth.	High-Power Laser Windows, X-ray Optics, Quantum Applications (NV centers).	SCD thickness up to 500 µm. Ra < 1 nm polishing.
Electronic Grade SCD	High-purity SCD optimized for charge carrier mobility and high breakdown voltage.	Particle Detectors (requiring high CCE), High-Power Diodes (SBDs).	Custom SCD plates, precise thickness control (0.1 µm to 500 µm).
Boron-Doped Diamond (BDD)	Conductive diamond material where defect control is critical for device performance (e.g., SBDs).	Electrochemistry, High-Frequency Electronics, Thermal Management.	Custom BDD synthesis and metalization services.
Large-Area PCD	Polycrystalline material offering large dimensions and high thermal conductivity.	High-Pressure Anvils, Large-Area Detectors, Heat Spreaders.	Plates up to 125 mm diameter. Substrates up to 10 mm thick.

Customization Potential for Research Replication

The review highlights the necessity of precise material specifications, particularly regarding dimensions, orientation, and surface quality. 6CCVD offers comprehensive customization capabilities:

Custom Dimensions and Thickness: We provide SCD and PCD plates in custom sizes, including large-area PCD wafers up to 125 mm, and SCD substrates up to 10 mm thick, exceeding typical research requirements.
Ultra-Low Roughness Polishing: Achieving defect-free growth requires pristine substrate surfaces. 6CCVD guarantees ultra-smooth polishing:
- SCD: Ra < 1 nm
- Inch-Size PCD: Ra < 5 nm
Advanced Metalization Services: For electronic device fabrication (e.g., Schottky Barrier Diodes (SBDs) mentioned in the paper), 6CCVD offers in-house deposition of standard and custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu.
Orientation and Geometry: We supply SCD plates cut to specific crystallographic orientations ((100), (110), (111)) and custom geometries required for advanced XRT and RCM studies.

Engineering Support & Global Logistics

6CCVD’s in-house PhD team specializes in diamond material science and defect engineering. We provide authoritative support to researchers and engineers:

Material Selection Consultation: Our experts assist in selecting the optimal SCD or PCD grade to minimize defects (dislocations, stacking faults, strain) based on the specific application (e.g., high-power electronics vs. X-ray optics).
Growth Recipe Optimization: We consult on substrate preparation and material specifications necessary for achieving low-dislocation epitaxial layers, addressing the critical challenge of defect propagation from the substrate interface.
Global Supply Chain: We ensure reliable, global delivery of custom diamond materials, with DDU (Delivered Duty Unpaid) as the default shipping method and DDP (Delivered Duty Paid) available upon request.

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

View Original Abstract

In this review, the X-ray topography results of various types of single crystal diamonds (SCDs) are reported. Dislocations and dislocation bundles are present in all types of SCDs, the only exception being type IIa high-pressure, high-temperature (HPHT) SCDs. The technology of growing HPHT type IIa SCDs has advanced to a level where the samples show almost no dislocations or dislocation bundles. However, very few groups appear to have perfected the process of HPHT growth of type IIa SCDs. There appears to be a characteristic difference in the dislocations present in type Ib HPHT and chemical vapor deposited (CVD) SCDs. The dislocations in CVD SCDs are mostly in aggregate form, while in HPHT type Ib diamonds there are line dislocations which propagate in <111> or <112> directions. The CVD SCDs growth appears to be in the early stage in terms of the control of dislocations and dislocation bundles, compared to other semiconductor wafers. The dislocations and dislocation bundles and aggregates in SCDs limit their applications in electronic and optical devices. For instance, high-power laser windows must have low dislocations and dislocation bundles. For electronic devices such as high-power diodes, dislocations reduce the breakdown voltage of SCDs, limiting their applications. The knowledge of dislocations, their identification and their origin are, therefore, of utmost importance for the applications of SCDs, be they HPHT or CVD grown.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst13040657

References

2017 - Synchrotron Bragg diffraction imaging characterization of synthetic diamond crystals for optical and electronic power devices application [Crossref]
2016 - Impact of impurities and crystal defects on the performance of CVD diamond detectors [Crossref]
2010 - Diamond detectors for hadron physics research [Crossref]
2017 - Thick CVD diamond films grown on high-quality type IIa HPHT diamond substrates from New Diamond Technology [Crossref]
2016 - Monocrystalline CVD diamond optics for high power applications
2021 - Recent progress in diamond radiation detectors [Crossref]
2018 - Multiphoton Upconversion Emission from Diamond Single Crystal [Crossref]
2017 - An Affordable Wet Chemical Route to Grow Conducting Hybrid Graphite-Diamond Nanowires: Demonstration by A Single nanowire Device [Crossref]