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

Executive Summary

This review analyzes the crystalline perfection and defect structures (dislocations, bundles, and aggregates) in various single crystal diamonds (SCDs) using Synchrotron X-ray Topography (XRT) and Rocking Curve Mapping (RCM).

Quality Benchmark: Type IIa High-Pressure, High-Temperature (HPHT) SCDs exhibit the highest crystalline perfection, showing almost no dislocations or stacking faults, achieving FWHM values near the theoretical minimum (~1 arc sec).
Type Ib HPHT Defects: These crystals contain line dislocations propagating along the <111> or <112> directions, often linked to high substitutional nitrogen (N) concentrations (tens to hundreds ppm).
CVD SCD Complexity: Chemical Vapor Deposition (CVD) SCDs show a more complex defect structure, including line dislocations, bundles, and large dislocation aggregates (clusters), which are largely absent in HPHT diamonds.
Defect Origin: Dislocations in both Type Ib HPHT and CVD SCDs primarily originate at the seed/substrate interface and propagate into the growing layer, often traveling within angular cones (20-30° in CVD).
Impact on Performance: High dislocation density and bundles severely limit applications, reducing breakdown voltage in diodes and deteriorating charge collection efficiency (CCE) in particle detectors.
Future Direction: CVD growth technology is considered in its early stages regarding defect control; achieving dislocation-free CVD SCDs requires detailed optimization and the use of near-perfect Type IIa HPHT substrates.

Technical Specifications

Parameter	Value	Unit	Context
CVD Feed Gas Purity	greater than 6N	%	Required for advanced applications
Nitrogen Impurity (Type IIa HPHT)	Sub-parts per billion	ppb	Achieved using N getters and pure catalysts
Nitrogen Impurity (Type Ib HPHT)	Tens to hundreds	ppm	Substitutional form (P1 center)
Natural ¹³C Content	~1% (10²¹-10²²)	atoms	Present in natural CH₄ used for CVD growth
Birefringence Requirement	less than 10^-4	N/A	High-power laser windows
RCM FWHM (Type IIa HPHT)	~1	arc sec	Near theoretical minimum (highest quality)
RCM FWHM (Type Ib HPHT)	4 to 8	arc sec	Typical range for yellow-brown crystals
RCM FWHM (CVD SCDs, high defect)	10 to 40	arc sec	Indicates high density of aggregates/bundles
RCM FWHM (¹³C Doped CVD)	15 to 45	arc sec	Increased strain due to ¹³C doping (R=0.24)
Dislocation Propagation Angle (CVD)	20-30	degrees	Angular cones originating from substrate
XRT Spatial Resolution (CHESS C1)	3	µm	Capability of the synchrotron setup
XRT Angular Resolution (CHESS C1)	2	micro-radians	Capability of the synchrotron setup
CVD Substrate Size (Typical)	5-6	mm	Larger than HPHT seeds
HPHT Seed Size (Typical)	0.1-0.2	mm	Used for HPHT growth

Key Methodologies

The crystalline perfection and defect mapping of SCDs were primarily conducted using Synchrotron X-ray Topography (XRT) techniques, often performed at facilities like the Cornell High Energy Synchrotron Source (CHESS).

Microwave Plasma Chemical Vapor Deposition (MPCVD) Growth: SCDs are grown using CH₄ and H₂ gases (greater than 6N purity) on selected substrates, typically Type Ib HPHT plates. Growth occurs in a cuboid shape.
High-Pressure, High-Temperature (HPHT) Synthesis: SCDs are grown using a metal catalyst (Fe, Ni, or Co) on a small seed crystal (0.1-0.2 mm). Type Ib crystals incorporate N impurities, while Type IIa crystals are grown using N-getters and pure materials to achieve sub-ppb N concentration.
Synchrotron X-ray Rocking Curve Mapping (RCM):
- The entire crystal is illuminated with a monochromatic X-ray beam (e.g., 15 keV).
- A series of 2D images are captured while scanning the sample around the Bragg angle (θ).
- The Full Width at Half Maximum (FWHM) of the rocking curve is calculated for every pixel, generating an FWHM map. Higher FWHM values directly correlate with higher concentrations of dislocations and strain.
Monochromatic X-ray Topography (XRT):
- The sample is illuminated at a specific Bragg angle corresponding to a crystal plane (e.g., (404) or (220)).
- Dislocations and stacking faults appear as dark contrast lines or bands on a grey background, allowing direct visualization of defect propagation.
White-Beam XRT Imaging:
- The sample is illuminated perpendicular to the incidence direction of a continuous X-ray beam.
- This technique generates images showing dislocations, bundles, and stacking faults with different contrasts, though resolution may be lower than monochromatic XRT.
Crystallographic Plane Analysis: RCM and XRT are used to map defects across various planes, including (111), (220), and (400), to determine defect orientation and density within different growth sectors.

Commercial Applications

The control and elimination of dislocations in SCDs are critical for high-performance applications across several engineering sectors:

Application Sector	Requirement/Benefit	SCD Type Preference
High-Power Electronics	High breakdown voltage; reduced internal strain. Dislocations reduce breakdown voltage in Schottky Barrier Diodes (SBDs).	Type IIa HPHT (low defect density)
High-Power Laser Optics	Low birefringence (less than 10^-4) and high optical quality. Dislocations and strain degrade optical properties.	Type IIa HPHT
Radiation/Particle Detectors	High Charge Collection Efficiency (CCE). Dislocation bundles generate internal strain and inhibit CCE.	Low-defect CVD SCDs (if perfected) or Type IIa HPHT
X-ray Monochromators	Low strain and high crystalline perfection (radius of curvature greater than 30 m).	Selected Type IIa HPHT or selected CVD SCDs
High-Pressure Anvils	Low internal strain and high resilience (e.g., Multimegabar pressure cells).	Type IIa HPHT
Quantum Electronics	Requires extremely low defect density for stable N-V centers and spin coherence.	Type IIa HPHT (for seed material)
Gemstones	High clarity (D color) and absence of inclusions/defects.	Type IIa HPHT

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]