Impact of Nitrogen, Boron and Phosphorus Impurities on the Electronic Structure of Diamond Probed by X-ray Spectroscopies

At a Glance

Metadata	Details
Publication Date	2021-03-09
Journal	C – Journal of Carbon Research
Authors	Sneha Choudhury, Ronny Golnak, Christian Schulz, Klaus Lieutenant, N. Tranchant
Institutions	Freie Universität Berlin, Centre National de la Recherche Scientifique
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Impact of Impurities on Diamond Electronic Structure

This document analyzes the research paper “Impact of Nitrogen, Boron and Phosphorus Impurities on the Electronic Structure of Diamond Probed by X-ray Spectroscopies” to highlight 6CCVD’s capabilities in supplying advanced MPCVD diamond materials for similar high-level research and engineering applications.

Executive Summary

The study provides critical insights into tailoring the electronic properties of single crystal diamond (SCD) through controlled doping, a process central to applications in electron emission, high-power electronics, and quantum technologies.

Core Achievement: Comprehensive comparison of occupied and unoccupied electronic states in Boron (B), Phosphorus (P), and Nitrogen (N) doped SCD using complementary soft X-ray spectroscopies (XAS, XES, XPS).
Methodology: B-SCD, P-SCD, and N-SCD epilayers were successfully grown using Microwave Plasma Chemical Vapor Deposition (MPCVD), confirming 6CCVD’s core expertise.
Key Finding (Unoccupied States): New electronic states were observed near the Conduction Band Minimum (CBM) and Valence Band Maximum (VBM) for B-SCD and P-SCD, crucial for tuning visible light absorption and electron emission.
Exciton Reduction: Impurity incorporation (B, P, N) significantly reduced the intensity of the diamond core exciton peak (289.3 eV), demonstrating sensitivity to lattice defects.
Surface Sensitivity: Surface-sensitive XPS confirmed that the occupied electronic states are highly susceptible to surface chemistry, reconstruction, and doping concentration, emphasizing the need for precise surface engineering (e.g., H-termination).
Material Relevance: The research validates the use of high-quality, custom-doped MPCVD SCD for fundamental studies aimed at developing next-generation diamond devices.

Technical Specifications

The following hard data points were extracted from the MPCVD growth recipes and characterization results detailed in the paper.

Parameter	Value	Unit	Context
P-SCD Growth Temperature	~1000	°C	MPCVD Epilayer Growth
N-SCD Growth Temperature	~900	°C	MPCVD Epilayer Growth
P-SCD Microwave Power	2.1	kW	Ellipsoidal MPCVD Reactor
N-SCD Microwave Power	630	W	MPCVD Reactor
P-SCD Growth Pressure	190	mbar	High-pressure growth regime
N-SCD Growth Pressure	100	mbar	Standard growth regime
N-SCD Epilayer Thickness	19	µm	Measured by SIMS
Boron Concentration ([B])	2.7 x 10²⁰	atoms/cm³	B-SCD (1500 ppm)
Phosphorus Concentration ([P])	8.0 x 10¹⁹	atoms/cm³	P-SCD (400 ppm)
Nitrogen Concentration ([N])	4.9 x 10¹⁸	atoms/cm³	N-SCD (30 ppm)
Diamond Bandgap (XAS/XES)	5.5	eV	Confirmed by VBM (284.0 eV) and CBM (289.5 eV)
Core Exciton Peak	289.3	eV	Feature III in TEY-XAS

Key Methodologies

The following steps outline the critical material preparation and characterization techniques used to achieve the reported results.

Substrate Preparation: Undoped <111> SCD substrates (for P-SCD) and HPHT <100> Sumitomo substrates (for N-SCD) were used.
P-SCD Epilayer Growth (MPCVD):
- Source Gases: H₂, CH₄, and Trimethylphosphine (P(CH₃)₃/H₂ = 4500 ppm).
- Gas Ratios: CH₄/H₂ = 0.13%; P/C = 20%.
- Conditions: 190 mbar pressure, 2.1 kW power, ~1000 °C growth temperature.
N-SCD Epilayer Growth (MPCVD):
- Source Gases: H₂ (95 vol%), CH₄ (4 vol%), N₂ (1 vol%).
- Conditions: 100 mbar pressure, 630 W power, ~900 °C growth temperature.
- Total Flow: 202 standard cubic centimeters per minute (SCCM).
Chemical Cleaning: All samples underwent thorough cleaning in a hotplate mixture of sulfuric and nitric acid (3:1 ratio) for 1.5 hours at 250 °C.
Surface Termination: Surface hydrogenation was performed in an H₂ plasma at 750 °C for 30 minutes in the MPCVD reactor.
Impurity Quantification: Secondary Ion Mass Spectrometry (SIMS) was used to measure depth profiles and absolute concentrations of B, P, and N.
Spectroscopic Analysis: Synchrotron-based soft X-ray techniques were employed:
- XAS (X-ray Absorption Spectroscopy) using Total Electron Yield (TEY, surface-sensitive) and Partial Fluorescence Yield (PFY, bulk-sensitive).
- XES (X-ray Emission Spectroscopy) and XPS (X-ray Photoemission Spectroscopy) for occupied state analysis.

6CCVD Solutions & Capabilities

This research demonstrates the critical role of highly controlled MPCVD growth and precise doping in achieving tailored electronic properties in diamond. 6CCVD is uniquely positioned to supply the custom materials required to replicate or advance this work, supporting engineers and scientists globally.

Applicable Materials

To replicate the high-quality, doped single crystal diamond (SCD) used in this study, 6CCVD recommends the following materials from our catalog:

Research Requirement	6CCVD Material Solution	Key Specification Match
Boron Doping (p-type)	Heavy Boron Doped Diamond (BDD)	Custom B concentration up to 10²¹ at/cm³ (matching 1500 ppm B-SCD).
Phosphorus Doping (n-type)	Custom P-Doped SCD (P-SCD)	Specialized MPCVD recipe development to achieve precise P concentrations (e.g., 400 ppm) and <111> orientation growth.
Nitrogen Doping (n-type)	Custom N-Doped SCD (N-SCD)	Controlled N₂ gas flow integration into the MPCVD process to achieve low concentrations (e.g., 30 ppm) for specific defect engineering.
Undoped Substrates	High Purity Optical Grade SCD	Used as the base material for epitaxial growth, ensuring minimal background impurities.

Customization Potential

The success of this research hinges on precise control over doping concentration, epilayer thickness, and surface preparation—all core competencies of 6CCVD.

Doping Control: 6CCVD specializes in custom MPCVD recipes, allowing researchers to specify dopant concentrations (B, P, N) across the full range investigated (30 ppm to 1500 ppm and beyond) for targeted electronic structure tuning.
Dimension and Thickness: The paper used 19 µm epilayers. 6CCVD offers:
- SCD and PCD plates/wafers up to 125 mm in diameter.
- Custom thickness control for SCD epilayers from 0.1 µm up to 500 µm.
Surface Engineering: The study utilized H₂ plasma termination. 6CCVD provides:
- Ultra-smooth polishing (Ra < 1 nm for SCD) prior to growth or characterization.
- Custom surface terminations (H-terminated, O-terminated) to control surface-sensitive electronic states probed by XPS/TEY-XAS.
Metalization Services: While not the focus of this paper, future device integration (e.g., contacts for electron emission devices) requires metalization. 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu layers.

Engineering Support

The complexity of correlating bulk (PFY-XAS, XES) and surface (TEY-XAS, XPS) electronic states requires deep material expertise. 6CCVD’s in-house PhD team provides consultative support for projects focused on:

Electron Field Emission: Assisting with material selection and doping profiles to optimize CBM/VBM states for enhanced electron emission efficiency.
High Power Electronics: Designing materials with specific defect levels and controlled conductivity (p-type BDD or n-type P/N-SCD) for device fabrication.
Quantum Defect Engineering: Providing ultra-pure SCD or precisely doped materials necessary for creating stable color centers or quantum emitters.

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

View Original Abstract

Doping diamond with boron, nitrogen or phosphorus enables a fine tuning of its electronic properties, which is particularly relevant for applications involving electron emission. However, the chemical nature of the doping sites and its correlation with electron emission properties remain to be clarified. In this work, we applied soft X-ray spectroscopy techniques to probe occupied and unoccupied electronic states in undoped, boron-, phosphorus- and nitrogen-containing single crystal diamonds. X-ray absorption, X-ray emission and X-ray photoemission spectroscopies, performed at the carbon K-edge, provide a full picture of new electronic states created by impurities in diamond. The different probing depths of fluorescence- and electron-based detection techniques enable a comparison between surface and bulk contributions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/c7010028

References

2013 - Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction [Crossref]
2014 - Selective Photoelectrochemical Reduction of Aqueous CO2 to CO by Solvated Electrons [Crossref]
2018 - Combining nanostructuration with boron doping to alter sub band gap acceptor states in diamond materials [Crossref]
2020 - Nanostructured Boron Doped Diamond Electrodes with Increased Reactivity for Solar-Driven CO2 Reduction in Room Temperature Ionic Liquids [Crossref]
2012 - Electronic Structure of Diamond Surfaces Functionalized by Ru(tpy)2 [Crossref]
2014 - Functionalization of Boron-Doped Nanocrystalline Diamond with N3 Dye Molecules [Crossref]
2018 - Enhanced Photocatalytic Activity of Diamond Thin Films Using Embedded Ag Nanoparticles [Crossref]
1995 - Defect-enhanced electron field emission from chemical vapor deposited diamond [Crossref]
1996 - Comparison of electric field emission from nitrogen-doped, type Ib diamond, and boron-doped diamond [Crossref]