Boron-doping effects on local structures of semiconducting ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films fabricated via coaxial arc plasma - an x-ray absorption spectroscopic study

At a Glance

Metadata	Details
Publication Date	2021-06-09
Journal	Semiconductor Science and Technology
Authors	Naofumi Nishikawa
Institutions	Kyushu University, Japan Advanced Institute of Science and Technology
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron-Doping Effects in Semiconducting Diamond Films

Executive Summary

This analysis focuses on the structural and chemical bonding effects of boron doping in Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon (B-UNCD/a-C:H) composite thin films, highlighting their potential for deep-UV photodetector applications.

Target Application: Deep-UV photodetectors, leveraging the material’s high light absorption coefficient (> 10⁵ cm^-1) in the 3 to 6 eV photon energy range.
Material Composition: Composite films consisting of UNCD grains embedded in an amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) matrix.
Doping Mechanism: Boron acts as the p-type dopant, achieving a relatively low activation energy of 0.37 eV, crucial for semiconducting behavior.
Key Structural Finding ($\sigma^*$ C-B): Near-Edge X-ray Absorption Fine Structure (NEXAFS) confirmed that boron preferentially forms $\sigma^*$ C-B bonds on the UNCD grain surfaces, substituting hydrogen atoms at grain boundaries (GBs).
Performance Correlation: The formation of these $\sigma^*$ C-B bonds is directly correlated with a drastic enhancement in electrical conductivity, reaching up to 2 x 10^-1 $\Omega$^-1cm^-1.
Structural Distortion: Low-level doping (0.1 at. %) causes initial structural distortion and increases unstable $\pi^$ C=C bonds, while higher doping stabilizes the structure by forming the desired $\sigma^$ C-B bonds.
6CCVD Value Proposition: 6CCVD offers high-quality, highly controlled Boron-Doped Diamond (BDD) via MPCVD, providing superior crystalline quality and performance stability for replicating and advancing this UV photodetector research.

Technical Specifications

The following hard data points were extracted from the experimental procedures and results concerning the B-UNCD/a-C:H films:

Parameter	Value	Unit	Context
Fabrication Method	Coaxial Arc Plasma Deposition (CAPD)	N/A	Physical Vapor Deposition (PVD) technique
Substrate Temperature	550	°C	Deposition temperature
Hydrogen Pressure	53.3	Pa	Operating pressure during deposition
Base Pressure (Vacuum)	10^-5	Pa	Chamber evacuation target
Boron Doping Concentration (Target)	0 to 10	at. %	Boron content in graphite targets
Light Absorption Coefficient	> 10⁵	cm^-1	High absorption in the 3 to 6 eV photon energy range
Boron Activation Energy	0.37	eV	Relatively low energy for p-type conduction
Enhanced Electrical Conductivity	Up to 2 x 10^-1	$\Omega$^-1cm^-1	Achieved with sufficient boron doping (compared to 2 x 10^-7 $\Omega$^-1cm^-1 for undoped)
Indirect Optical Bandgap	1.7	eV	Stemming from amorphous regions
Direct Optical Bandgap	2.9	eV	Attributed to grain boundaries (GBs)
$\sigma^*$ C-B Resonance Energy	286.9	eV	Observed in NEXAFS C K-edge spectra

Key Methodologies

The B-UNCD/a-C:H films were fabricated and analyzed using the following key steps:

Film Fabrication (CAPD): Thin films were deposited using a Coaxial Arc Plasma Deposition (CAPD) system, a PVD technique, onto insulating Si substrates (resistivity > 10 k$\Omega$ $\cdot$ cm).
Doping Control: Graphite targets were blended with specific Boron concentrations (0, 0.1, 1.0, 5.0, and 10 at. %) to control the dopant level in the resulting films.
Process Parameters: Deposition was conducted under a hydrogen pressure of 53.3 Pa at a fixed substrate temperature of 550 °C.
Structural Analysis (NEXAFS): Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was performed at the Kyushu Synchrotron Research Center to obtain B K-edge and C K-edge spectra.
Bonding Quantification: C K-edge spectra were deconvoluted using Gaussian and arctangent functions to quantitatively analyze carbon hybridization states, including $\pi^$ C=C, $\sigma^$ C-H, $\sigma^$ C-C, and the critical $\sigma^$ C-B bonds.
Impurity Confirmation (XPS): X-ray Photoelectron Spectroscopy (XPS) survey scans were used to confirm the incorporation of boron and the presence of oxygen impurities, which were found to be involved in boron-oxide formation at the film surface.

6CCVD Solutions & Capabilities

The research demonstrates the viability of boron-doped diamond materials for high-performance semiconducting devices, particularly deep-UV photodetectors. 6CCVD specializes in high-purity, highly controllable MPCVD diamond, offering superior alternatives to the composite UNCD/a-C:H films used in this study.

Research Requirement	6CCVD Material Solution	6CCVD Technical Capability
P-Type Semiconductor Material	Boron-Doped Diamond (BDD)	6CCVD provides high-quality BDD films (SCD or PCD) with precise control over boron concentration, ensuring stable p-type conduction and low activation energy (0.37 eV).
High-Performance UV Detection	Optical Grade SCD/PCD	Our MPCVD diamond offers superior crystalline quality and purity, maximizing the intrinsic wide bandgap (5.47 eV) properties required for stable, high-sensitivity deep-UV detection.
Custom Doping & Structure Study	Custom BDD Synthesis	We can replicate the target doping range (0.1 to 10 at. %) used in the paper, but within a purer, more structurally defined MPCVD matrix, allowing researchers to isolate the effects of $\sigma^*$ C-B bonding without the complexities of the amorphous carbon matrix.
Thin Film Device Fabrication	Thickness Control (0.1 $\mu$m to 500 $\mu$m)	6CCVD guarantees precise thickness control for both SCD and PCD layers, essential for optimizing carrier transport pathways and light absorption depth in photodetector architectures.
Large Area Scaling	PCD Wafers up to 125 mm	While the paper used small experimental samples, 6CCVD supports scaling up research to commercial production volumes with inch-size PCD wafers (up to 125 mm diameter).
Heterojunction/Electrode Integration	Custom Metalization Services	We offer in-house deposition of standard contacts (Au, Pt, Pd, Ti, W, Cu), enabling rapid prototyping of p-n heterojunction diodes or Schottky barrier devices, similar to those referenced in the paper (e.g., p-BDD/n-Si).
Surface Quality for Analysis	Polishing (Ra < 1 nm for SCD)	High-quality polishing ensures minimal surface defects and roughness, critical for advanced spectroscopic analysis (NEXAFS, XPS) and reliable device performance.

Engineering Support

The findings regarding the preferential formation of $\sigma^*$ C-B bonds at grain boundaries are highly relevant for optimizing polycrystalline diamond devices. 6CCVD’s in-house PhD team can assist engineers and scientists with material selection and design for similar UV Photodetector projects, ensuring the optimal balance between doping concentration, crystallinity, and surface termination.

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

View Original Abstract

Abstract Ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films synthesized via coaxial arc plasma possess a marked structural feature of diamond grains embedded in an amorphous carbon and a hydrogenated amorphous carbon matrix which are the largest constituents of the films. Since the amorphous nature yields much larger light absorption coefficients as well as a generation source of photo-induced carriers with UV rays, these films can be potential candidates for deep-UV photodetector applications. From some previous studies p-type conduction of the films has been realized by doping boron in experimental conditions. In addition, their optical and electrical characteristics were investigated previously. However, the bonding structures which largely affect the physical properties of the devices have not been investigated. In this work, near-edge x-ray absorption fine structure spectroscopy characterizations are carried out. The result reveals that a bonding state σ * C-B of diamond surfaces is formed preferentially and structural distortion is caused at an early stage of boron-doping. Further doping into the films lessens the amount of unsaturated bonds such as π * C≡C, which may be a cause of the device performance degradations. Our work suggests a fundamental case model of boron-doping effects on a local structure of the film.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1361-6641/ac09d0

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