Correlated Electrical Conductivities to Chemical Configurations of Nitrogenated Nanocrystalline Diamond Films

At a Glance

Metadata	Details
Publication Date	2022-03-03
Journal	Nanomaterials
Authors	Abdelrahman Zkria, Hiroki Gima, Eslam Abubakr, Ashraf M. Mahmoud, Ariful Haque
Institutions	Kyushu University, Texas State University
Citations	16
Analysis	Full AI Review Included

Technical Analysis and Documentation: Nitrogenated Nanocrystalline Diamond Films

Executive Summary

This documentation analyzes the synthesis and characterization of nitrogenated Nanocrystalline Diamond (NCD) films, confirming their viability as n-type semiconductors for optoelectronic and high-frequency applications.

Core Achievement: Successful synthesis of n-type NCD films via Physical Vapor Deposition (PVD), demonstrating enhanced electrical conductivity directly proportional to nitrogen doping concentration (up to 8 at.%).
Electrical Performance: Electrical conductivity increased significantly with doping, correlating with a reduction in activation energy (E_a) from 123 meV (3 at.%) to 108 meV (8 at.%).
Doping Mechanism: Sensitive spectroscopic analysis (NEXAFS) confirmed that nitrogen incorporation primarily forms π*C=N bonds within the grain boundaries (GBs), which are responsible for generating free electrons and the observed n-type conductivity.
Morphology: Films exhibited excellent uniformity and low surface roughness (RMS 8 nm) at a thickness of 400 nm, suitable for thin-film device integration.
6CCVD Value Proposition: While the paper used PVD, 6CCVD specializes in high-quality MPCVD diamond. We offer custom Polycrystalline Diamond (PCD) wafers and advanced metalization services necessary to replicate, scale, and integrate these findings into commercial semiconductor devices.

Technical Specifications

The following hard data points were extracted from the research regarding material properties and performance:

Parameter	Value	Unit	Context
Diamond Bandgap	5.45	eV	Intrinsic property
Diamond Thermal Conductivity	3320	W m^-1 K^-1	Intrinsic property
Film Thickness	400	nm	N-doped NCD layer
Substrate Temperature	550	°C	During CAPG deposition
Deposition Pressure	53	Pa	Final deposition pressure
RMS Surface Roughness	8	nm	Measured by AFM on NCD film (Ra < 5 nm achievable by 6CCVD)
Nitrogen Content (Max)	8	at.%	Achieved at I_N/H = 1.5
Electrical Conductivity (Max)	~10¹	S/cm	Measured at 500 K for 8 at.% NCD
Activation Energy (E_a, Min)	108	meV	For 8 at.% N-doped NCD film
Activation Energy (E_a, Max)	123	meV	For 3 at.% N-doped NCD film
Key Bonding Structure	π*C=N	-	Free electron generation at grain boundaries

Key Methodologies

The Nanocrystalline Diamond Composite films were synthesized and characterized using the following primary steps:

Substrate Preparation: Commercial p-type mirror-polished Si (100) substrates were cleaned using standard solvent procedures (acetone, methanol, DI water).
Deposition Technique: Films were grown using a Coaxial Arc Plasma Gun (CAPG) Physical Vapor Deposition (PVD) system, utilizing a bulk graphite target (99.9% purity).
Process Parameters: The substrate temperature was maintained at 550 °C. The base pressure was evacuated to <10^-5 Pa, and the final deposition pressure was held at 53 Pa.
Plasma Excitation: The plasma was sustained using an applied voltage of 100 V and a discharge pulse repetition rate of 5 Hz.
Doping Control: Nitrogen doping was achieved by introducing mixed H₂ and N₂ gases, varying the inflow ratio (I_N/H) from 0.3 to 1.5, resulting in nitrogen contents ranging from 3 at.% to 8 at.%.
Structural Characterization: High-resolution SEM (HRSEM) and AFM were used for morphology. Chemical composition and bonding were analyzed using synchrotron-based X-ray Photoemission Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine-Structure Spectroscopy (NEXAFS).
Electrical Measurement: Electrical conductivities were evaluated using the van der Pauw method on samples prepared in well-defined squared geometries.

6CCVD Solutions & Capabilities

6CCVD is positioned to support and advance research into diamond semiconductor devices, offering high-quality MPCVD materials and custom engineering services that meet or exceed the requirements demonstrated in this study.

Applicable Materials

While the research utilized PVD-grown NCD, 6CCVD provides superior, highly controllable MPCVD materials ideal for scaling semiconductor applications:

Material	Description & Application	6CCVD Capability
Polycrystalline Diamond (PCD)	Ideal for replicating NCD structures with superior purity and thickness control. Suitable for large-area, high-power devices.	Wafers up to 125 mm diameter. Thicknesses from 0.1 µm to 500 µm. Polishing to Ra < 5 nm.
Boron-Doped Diamond (BDD)	Essential for comparative studies or fabricating p-n heterojunctions (as referenced in prior work). Provides stable, high-conductivity p-type layers.	Custom doping levels available for heavy or light doping. Available in SCD or PCD formats.
Single Crystal Diamond (SCD)	For high-frequency or quantum applications requiring minimal grain boundaries and ultra-low defect density.	High-purity electronic grade material. Thicknesses from 0.1 µm to 500 µm. Polishing to Ra < 1 nm.

Customization Potential

The success of this research relies on precise film thickness, substrate integration, and robust electrical contacts. 6CCVD offers full customization to meet these engineering demands:

Custom Dimensions and Thickness: The paper used 400 nm films. 6CCVD can supply custom SCD and PCD films with precise thickness control ranging from 0.1 µm to 500 µm, and substrates up to 10 mm thick. We offer custom laser cutting for unique device geometries.
Substrate Integration: While the paper used Si (100), 6CCVD can grow diamond films on various substrates, including Si, Mo, and W, and provide custom substrate preparation.
Advanced Metalization: The electrical characterization required robust contacts (Pd electrodes were shown). 6CCVD offers internal metalization capabilities, including single or multi-layer stacks of Au, Pt, Pd, Ti, W, and Cu, optimized for ohmic contact formation on both n-type and p-type diamond.

Engineering Support

The correlation of chemical bonding (NEXAFS) to electrical performance is critical for developing reliable n-type diamond devices. 6CCVD’s in-house PhD team specializes in:

Material Selection: Assisting researchers in selecting the optimal diamond type (PCD vs. SCD) and doping strategy (N-doping simulation or BDD alternatives) for similar optoelectronic and high-frequency semiconductor device projects.
Surface Engineering: Providing expertise in surface termination and polishing (Ra < 1 nm for SCD) to minimize defects and optimize interfaces, crucial for enhancing device performance beyond the 8 nm RMS roughness reported here.
Global Logistics: Offering reliable global shipping (DDU default, DDP available) to ensure materials reach your lab quickly and safely.

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

View Original Abstract

Diamond is one of the fascinating films appropriate for optoelectronic applications due to its wide bandgap (5.45 eV), high thermal conductivity (3320 W m−1·K−1), and strong chemical stability. In this report, we synthesized a type of diamond film called nanocrystalline diamond (NCD) by employing a physical vapor deposition method. The synthesis process was performed in different ratios of nitrogen and hydrogen mixed gas atmospheres to form nitrogen-doped (n-type) NCD films. A high-resolution scanning electron microscope confirmed the nature of the deposited films to contain diamond nanograins embedded into the amorphous carbon matrix. Sensitive spectroscopic investigations, including X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS), were performed using a synchrotron beam. XPS spectra indicated that the nitrogen content in the film increased with the inflow ratio of nitrogen and hydrogen gas (IN/H). NEXAFS spectra revealed that the σC-C peak weakened, accompanied by a πC=N peak strengthened with nitrogen doping. This structural modification after nitrogen doping was found to generate unpaired electrons with the formation of C-N and C=N bonding in grain boundaries (GBs). The measured electrical conductivity increased with nitrogen content, which confirms the suggestion of structural investigations that nitrogen-doping generated free electrons at the GBs of the NCD films.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano12050854

References

2020 - Laser-Induced Phosphorus-Doped Conductive Layer Formation on Single-Crystal Diamond Surfaces [Crossref]
2020 - Low temperature synthesis of transparent conductive boron doped diamond films for optoelectronic applications: Role of hydrogen on the electrical properties [Crossref]
2022 - Materials Science in Semiconductor Processing Laser-induced novel ohmic contact formation for effective charge collection in diamond detectors [Crossref]
2021 - Infrared photodetectors based on multiwalled carbon nanotubes: Insights into the effect of nitrogen doping [Crossref]
2020 - Boosting Lithium Storage in Free-Standing Black Phosphorus Anode via Multifunction of Nanocellulose [Crossref]
2021 - Flexible electronics based on 2D transition metal dichalcogenides [Crossref]
2008 - On-state behaviour of diamond Schottky diodes [Crossref]