Direct imaging of boron segregation at dislocations in B -diamond heteroepitaxial films

At a Glance

Metadata	Details
Publication Date	2015-12-21
Journal	Nanoscale
Authors	Stuart Turner, Hosni Idrissi, André F. Sartori, S. Korneychuck, Y.-G. Lu
Institutions	University of Antwerp, University of North Carolina at Charlotte
Citations	23
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron Segregation in B:Diamond Films

Executive Summary

This research provides critical, atomic-scale insight into dopant behavior in heavily boron-doped diamond (BDD) heteroepitaxial films grown by Microwave Plasma Chemical Vapor Deposition (MPCVD). The findings are essential for optimizing diamond semiconductor performance and reliability.

Core Achievement: Direct imaging and chemical analysis of boron (B) segregation at individual dislocation cores in MPCVD B:diamond films using advanced STEM-EELS.
Material System: Heavily B-doped diamond (~1 µm thick) grown on an undoped diamond layer (~1 mm thick) on an Ir/YSZ/Si(001) stack.
Defect Analysis: Confirmed a high dislocation density (~2 x 10¹⁰ cm^-2), identifying both edge and mixed-type 45° dislocations.
Dopant Segregation: Boron concentration locally increases at dislocation cores, reaching up to 2.5 at% (compared to 1.0-1.5 at% bulk concentration).
Strain Correlation: Boron enrichment is non-symmetrical, specifically targeting the tensile strain field surrounding edge dislocations, confirming that lattice relaxation facilitates higher dopant incorporation.
Hybridization State: EELS fine structure analysis shows that boron at the dislocation core is partially substitutionally incorporated (tetrahedral) and partially present in a lower coordination state (sp²-like hybridization).
Implication for Devices: This intermittent segregation behavior strongly influences charge carrier transport and must be controlled for high-performance diamond semiconductor devices (e.g., high-power switches, radiation detectors).

Technical Specifications

The following hard data points were extracted from the analysis of the MPCVD B:diamond heteroepitaxial film:

Parameter	Value	Unit	Context
B-Doped Layer Thickness	~1	µm	Grown by MPCVD on undoped layer
Undoped Layer Thickness	~1	mm	Grown prior to BDD layer
Nominal Boron Content (Bulk)	1.0-1.5	at%	Corresponds to 1.8-2.7 x 10²¹ cm^-3
Local Boron Content (Dislocation Core)	Up to 2.5	at%	Measured via EELS
Dislocation Density	~2 x 10¹⁰	cm^-2	Measured via Weak-Beam Dark-Field TEM (WBDF)
B-Enriched Region Width	~2	nm	Width of the boron-rich region surrounding the core
Boron K-Edge Peak	190	eV	Used for EELS mapping
Carbon K-Edge Peak	285	eV	Used for EELS mapping
Dislocation Types Identified	Edge, Mixed 45°	N/A	Found in [001] oriented film
Spherical Aberration (Cs)	-12	µm	Used for Negative Cs Imaging (HRTEM)

Key Methodologies

The study relied on precise MPCVD growth techniques combined with state-of-the-art aberration-corrected microscopy and spectroscopy.

Substrate Preparation: Initial growth utilized an Ir/YSZ/Si(001) stack with a 6° off-axis tilt to promote heteroepitaxial growth.
Undoped Diamond Growth: A thick (~1 mm) undoped diamond layer was grown via MPCVD.
Substrate Removal: The Ir/YSZ/Si stack was removed using chemical/mechanical polishing and plasma etching to yield a freestanding, high-quality undoped diamond substrate.
B-Doped Layer Growth: A heavily B-doped layer (~1 µm) was grown on the back side of the undoped diamond using MPCVD.
Doping Parameters: Trimethylboron (TMB, B[CH₃]₃) was introduced into the gas phase, achieving a nominal B/C ratio of 980 ppm (corresponding to 42.763 ppm TMB).
Sample Thinning: Focused Ion Beam (FIB) milling was used to prepare electron-transparent cross-sectional and plan-view foils for TEM analysis.
Structural Characterization: Conventional and Weak-Beam Dark-Field (WBDF) Transmission Electron Microscopy (TEM) were employed to determine dislocation type (Burgers vector analysis) and measure dislocation density.
Chemical and Strain Mapping: Aberration-corrected High-Resolution (HR) ADF-STEM combined with spatially resolved Electron Energy-Loss Spectroscopy (EELS) was used to map B distribution and analyze the B-K edge fine structure. Geometrical Phase Analysis (GPA) was applied to HRTEM images to quantify local strain fields.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate, extend, and commercialize the findings of this research, particularly concerning defect engineering and controlled doping in BDD films.

Applicable Materials

To replicate or extend this research into functional devices, high-quality, heavily doped material is essential.

Heavy Boron Doped SCD (BDD): 6CCVD offers high-purity Single Crystal Diamond (SCD) wafers doped with Boron. Our BDD material provides the necessary p-type conductivity and can be tailored to match the high doping concentrations (10²¹ cm^-3 range) used in this study, crucial for applications like electrochemical sensing and superconductivity research.
Polycrystalline Diamond (PCD) Substrates: For large-area or cost-sensitive applications where the high dislocation density inherent to heteroepitaxy (as seen in the paper) is acceptable, 6CCVD supplies large-area PCD wafers up to 125mm in diameter.

Customization Potential

The success of this research hinges on precise material dimensions and advanced preparation techniques, areas where 6CCVD excels.

Requirement from Paper	6CCVD Customization Capability	Value Proposition
Precise Layer Thickness (1 µm BDD layer)	We offer SCD and PCD films with thickness control from 0.1 µm up to 500 µm, allowing researchers to precisely control the active layer depth for device fabrication or fundamental studies.	Enables exact replication of experimental parameters and optimization for specific device geometries (e.g., thin films for EELS/TEM).
Advanced Characterization Prep	We provide ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), which is critical for subsequent high-resolution TEM/STEM and EELS analysis (as performed in the paper).	Reduces sample preparation time and artifacts (like surface amorphization) that can interfere with atomic-scale imaging.
Device Integration (Future Need)	Custom Metalization Services: We offer in-house deposition of standard and custom metal stacks (Au, Pt, Pd, Ti, W, Cu) for ohmic or Schottky contacts.	Facilitates rapid transition from fundamental material study to functional device prototyping (e.g., high-power diodes or sensors).
Custom Dimensions	We supply plates and wafers in custom dimensions up to 125mm (PCD) and offer precision laser cutting services.	Supports scaling up research from small experimental samples to technologically relevant wafer sizes.

Engineering Support

The observed boron segregation to tensile strain fields is a fundamental challenge in diamond semiconductor engineering.

Defect Engineering Consultation: 6CCVD’s in-house PhD team specializes in MPCVD growth optimization, focusing on defect control and dopant activation. We can assist clients in selecting the optimal material grade (SCD vs. PCD) and growth recipe to minimize or manage the impact of B segregation for similar high-power switching, radiation detection, or electrochemical projects.
Material Selection for High-Performance: Understanding the interplay between B coordination (sp³ vs. sp²-like) and electrical properties is crucial. Our experts provide consultation on achieving the highest possible substitutional B incorporation for superior electrical performance.

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

View Original Abstract

A thin film of heavily B-doped diamond has been grown epitaxially by microwave plasma chemical vapor deposition on an undoped diamond layer, on top of a Ir/YSZ/Si(001) substrate stack, to study the boron segregation and boron environment at the dislocations present in the film. The density and nature of the dislocations were investigated by conventional and weak-beam dark-field transmission electron microscopy techniques, revealing the presence of two types of dislocations: edge and mixed-type 45° dislocations. The presence and distribution of B in the sample was studied using annular dark-field scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy. Using these techniques, a segregation of B at the dislocations in the film is evidenced, which is shown to be intermittent along the dislocation. A single edge-type dislocation was selected to study the distribution of the boron surrounding the dislocation core. By imaging this defect at atomic resolution, the boron is revealed to segregate towards the tensile strain field surrounding the edge-type dislocations. An investigation of the fine structure of the B-K edge at the dislocation core shows that the boron is partially substitutionally incorporated into the diamond lattice and partially present in a lower coordination (sp(2)-like hybridization).

Tech Support

Original Source

DOI: https://doi.org/10.1039/c5nr07535a