Laser vibrational excitation of radicals to prevent crystallinity degradation caused by boron doping in diamond

At a Glance

Metadata	Details
Publication Date	2021-01-20
Journal	Science Advances
Authors	Lisha Fan, Loïc Constantin, Zhipeng Wu, Kayleigh A. McElveen, X. G. Chen
Institutions	Sorbonne Université, Centre National de la Recherche Scientifique
Citations	15
Analysis	Full AI Review Included

Technical Documentation & Analysis: Laser Vibrational Excitation in BDD Growth

Source Paper: Fan et al., Sci. Adv. 2021; 7: eabc7547. Laser vibrational excitation of radicals to prevent crystallinity degradation caused by boron doping in diamond.

Executive Summary

This research demonstrates a breakthrough in synthesizing highly conductive, high-crystallinity Boron-Doped Diamond (BDD) films using laser-assisted Chemical Vapor Deposition (CVD). This method addresses the long-standing challenge of maintaining lattice integrity during heavy doping, a critical bottleneck in semiconductor diamond fabrication.

Novel Doping Control: Achieved superior BDD quality by introducing thermal non-equilibrium via resonant vibrational excitation of the growth-critical radical, Boron Dihydride ($\text{BH} _{2}$), using a $10.494 \text{ µm}$ $\text{CO} _{2}$ laser.
High Electrical Performance: Resulting BDD exhibited metallic-type conductivity with a high hole mobility of $55.6 \text{ cm} ^{2} \text{ V} ^{-1} \text{ s} ^{-1}$ and ultra-low resistivity of $28.1 \text{ milliohm-cm}$ at $300 \text{ K}$.
High Doping Density & Quality: Successfully incorporated a high B density ($4.3 \times 10^{21} \text{ cm} ^{-3}$) while maintaining superior crystallinity, confirmed by TEM showing sharp, non-diamond impurity-free grain boundaries.
Accelerated Growth: Demonstrated a rapid growth rate of $35 \text{ µm/hour}$, representing a 30 to 100-fold increase over traditional Hot Filament CVD (HFCVD) and Microwave Plasma-Enhanced CVD (MPCVD).
Enhanced Functionality: The highly crystalline and conductive BDD electrodes showed enhanced efficiency in non-enzymatic glucose sensing, validating the material’s potential for advanced electroanalytical devices.
Microscopic Control: The technique offers a pathway for “microscopic” control over doping chemistry, promising removal of bottlenecks in the wider semiconductor industry.

Technical Specifications

Hard data extracted from the research paper detailing the material properties and process parameters of the optimized BDD films (prepared at $21 \text{ W}$ absorbed laser power).

Parameter	Value	Unit	Context
Boron Concentration ([B])	$4.3 \times 10^{21}$	$\text{cm} ^{-3}$	Achieved with laser excitation (SIMS/Hall effect)
Film Resistivity ($\rho$)	28.1	milliohm-cm	Measured at $300 \text{ K}$ (Metallic conductivity)
Hall Hole Mobility ($\mu$)	55.6	$\text{cm} ^{2} \text{ V} ^{-1} \text{ s} ^{-1}$	Measured at $300 \text{ K}$ (High crystallinity confirmed)
Growth Rate	35	$\text{µm/hour}$	Laser-assisted Combustion CVD
Substrate Temperature	$780 \pm 10$	$\text{°C}$	During deposition
Laser Wavelength	10.494	$\text{µm}$	Resonant excitation of $\text{BH} _{2}$ bending mode ($\nu _{2}$)
Absorbed Laser Power (Optimal)	21	W	Corresponds to maximum crystallinity improvement
Working Potential Window (BDD)	Up to 2.9	V	Widened due to improved crystallinity
Commercial BDD Resistivity (Comparison)	4616	ohm-cm	Five orders of magnitude higher than optimized film

Key Methodologies

The experiment utilized a specialized laser-assisted combustion CVD setup to achieve non-equilibrium doping control.

CVD Setup: Open-air combustion CVD using an oxyacetylene flame.
Substrate Preparation: p-type silicon wafers ultrasonically seeded in a $5 \text{ nm}$ diamond slurry.
Gas Flows (Combustion): Acetylene ($\text{C} _{2}\text{H} _{2}$) at $1685 \text{ sccm}$ and Oxygen ($\text{O} _{2}$) at $1795 \text{ sccm}$.
Boron Source: Boric acid ($\text{H} _{3}\text{BO} _{3}$) methanol solution ($10 \text{ g/liter}$), introduced via a third acetylene line.
Doping Control: Boron source flow rate tuned from $0 \text{ to } 100 \text{ sccm}$ to control doping density.
Temperature Control: Substrate temperature maintained at $780 \pm 10 \text{°C}$ using a water-cooled three-axis moving stage.
Laser Excitation: A wavelength-tunable, continuous-wave $\text{CO} _{2}$ laser was used, tuned precisely to $10.494 \text{ µm}$ to match the fundamental vibrational quanta of the $\text{BH} _{2}$ bending mode.
Characterization: FESEM, micro-Raman spectroscopy, Hall effect measurement, SIMS, and high-resolution TEM were used to confirm morphology, crystallinity, electrical properties, and atomic structure.

6CCVD Solutions & Capabilities

The research successfully demonstrated that high-performance BDD requires not only high doping density but also exceptional crystallinity—a challenge 6CCVD is uniquely positioned to solve through advanced MPCVD material engineering and customization.

Applicable Materials

To replicate or extend this high-performance BDD research, engineers require materials that combine high conductivity with minimal lattice defects.

Boron-Doped Polycrystalline Diamond (BDD-PCD): 6CCVD offers heavy Boron-Doped PCD optimized for electrochemistry and sensing applications. Our PCD films are grown with high purity and controlled grain structure, providing the low resistivity and high surface area required for enhanced glucose sensing performance demonstrated in the paper.
High-Purity Single Crystal Diamond (SCD) Substrates: For applications requiring the absolute highest mobility or integration into complex electronic devices, 6CCVD supplies SCD substrates (up to $500 \text{ µm}$ thick) which can be custom-doped to achieve superior uniformity and defect control compared to polycrystalline films.

Customization Potential

The paper highlights the need for precise material specifications, including specific dimensions and integrated metal contacts for electrode fabrication. 6CCVD excels in delivering custom solutions that meet these stringent requirements.

Research Requirement	6CCVD Customization Service
Unique Dimensions	Custom Plates/Wafers up to 125 mm: While the study used small $5.0 \text{ mm} \times 5.0 \text{ mm}$ samples, 6CCVD can scale production to large-area PCD wafers (up to $125 \text{ mm}$) and custom-cut plates, facilitating industrial device manufacturing.
Specific Thicknesses	Precision Thickness Control: We offer BDD films in thicknesses ranging from $0.1 \text{ µm}$ (for thin-film devices) up to $500 \text{ µm}$ (for robust electrodes), and substrates up to $10 \text{ mm}$.
Electrode Integration	Internal Metalization Capabilities: The BDD electrodes require stable contacts. 6CCVD provides in-house metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing us to deliver fully metalized, ready-to-use BDD components.
Surface Finish	Ultra-Low Roughness Polishing: To ensure optimal electrochemical performance and integration, 6CCVD guarantees surface roughness (Ra) of < $5 \text{ nm}$ for inch-size PCD and < $1 \text{ nm}$ for SCD.

Engineering Support

The successful implementation of highly conductive, crystalline BDD for advanced applications like biosensing requires deep material science expertise. 6CCVD’s in-house $\text{PhD}$ engineering team specializes in optimizing diamond growth recipes to achieve specific electrical and structural properties.

Material Selection for Electrochemistry: Our experts can assist researchers and engineers in selecting the optimal BDD doping level and crystal structure (PCD vs. SCD) necessary to maximize charge transfer rates and working potential windows for similar electroanalytical and sensing projects.
Global Supply Chain: 6CCVD ensures reliable, global shipping (DDU default, DDP available) of highly sensitive diamond materials, supporting international research and development efforts.

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

View Original Abstract

An active, “microscopic,” laser-enabled control of energy coupling channel produces highly conductive and crystalline diamond.

Tech Support

Original Source

DOI: https://doi.org/10.1126/sciadv.abc7547