Characterization of boron-doped single-crystal diamond by electrophysical methods (review)
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Журнал технической физики |
| Authors | Zubkov V.I., Solomnikova A.V., Solomonov A.V., Koliadin A.V., Butler J.E. |
| Institutions | Saint Petersburg State Electrotechnical University, Almaz-Antey (Russia) |
| Citations | 3 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Boron-Doped Single-Crystal Diamond Characterization
Section titled “Technical Documentation & Analysis: Boron-Doped Single-Crystal Diamond Characterization”Executive Summary
Section titled “Executive Summary”This technical review validates the use of Admittance Spectroscopy (AS) and Capacitance-Voltage (C-V) methods for precise, non-destructive characterization of Boron-Doped Single-Crystal Diamond (BDD SCD) intended for advanced semiconductor applications.
- Core Achievement: Successful measurement and comparison of impurity concentration ($N_A$) via FTIR and majority charge carrier concentration ($p$) via C-V/AS across a wide doping range ($2 \cdot 10^{16}$ to $4 \cdot 10^{19}$ cm-3).
- Critical Material Property: Experimental confirmation that increasing boron concentration significantly reduces the hole activation energy ($E_A$) from 325 meV down to 100 meV, facilitating higher ionization degrees necessary for device operation.
- Methodology Validation: Admittance Spectroscopy is confirmed as the most effective diagnostic method, closely simulating the dynamic, non-equilibrium conditions found in active diamond semiconductor devices.
- Growth Techniques: Samples characterized included high-quality SCD grown by both HPHT (bulk plates) and MPCVD (epitaxial layers, 2-2.7 µm thick).
- Surface Quality: HPHT samples demonstrated excellent surface morphology with roughness (Ra) as low as 1-3 nm, crucial for subsequent metal contact deposition (e.g., Platinum Schottky barriers).
- Application Relevance: The findings provide a physical and technological foundation for developing next-generation diamond-based instruments for power electronics, optical devices, and biosensorics operating in extreme conditions.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Bandgap ($E_g$) | 5.45 | eV | Wide bandgap semiconductor |
| Boron Ionization Energy ($E_A$) (Reference) | 370 | meV | Weakly-doped diamond (Optical) |
| Measured $E_A$ Range (Admittance) | 325 to 100 | meV | SCD, dependent on $N_A$ concentration |
| Boron Concentration ($N_A$) Range Studied | $2 \cdot 10^{16}$ to $4 \cdot 10^{19}$ | cm-3 | Weakly to heavily doped SCD |
| Hopping Conduction Activation Energy ($E_A$) | 10-20 | meV | Observed for $N_A \ge 5 \cdot 10^{18}$ cm-3, T < 150 K |
| CVD Epitaxial Layer Thickness | 2.0 to 2.7 | µm | Boron-doped layers |
| HPHT Plate Thickness | 300 to 500 | µm | Bulk single-crystal plates |
| HPHT Surface Roughness (Ra) | 1-3 | nm | Excellent morphology for contact deposition |
| CVD Reactor Operating Frequency | 2.45 | GHz | Magnetron UHF radiation |
| Substrate Temperature (CVD) | 700-1100 | °C | Diamond film deposition |
| Measurement Temperature Range | 15-475 | K | Cryogenic probe station |
| Test Signal Frequency Range (AS/C-V) | 100 Hz-2 | MHz | Admittance Spectroscopy |
Key Methodologies
Section titled “Key Methodologies”The research employed a combination of synthesis and advanced electrophysical characterization techniques to analyze the BDD SCD samples:
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Synthesis Methods:
- HPHT (High Pressure High Temperature): Used to grow bulk single-crystal diamond plates (0.3-0.5 mm thick) from cuboctahedral seedings at $1400 \pm 50$ °C and 5-6 GPa pressure. Boron was added directly to the growth cell.
- MPCVD (Microwave Plasma Chemical Vapor Deposition): Used to grow epitaxial layers (2.0-2.7 µm thick) on (100) HPHT substrates using H2 + CH4 gas mixture and trimethyl borate B(OCH3)3 dissolved in ethanol for boron doping.
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Contact Deposition:
- Platinum (Pt) metal contacts were deposited via magnetron spraying to form Schottky diodes. Ohmic contacts were annealed at 300 °C; rectifying contacts deposited at 70 °C through a 130 µm mask.
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Impurity Concentration Measurement (Static):
- FTIR Spectroscopy (Fourier Transform Infrared Spectroscopy): Used to determine the depth-averaged concentration of the partially compensated boron impurity ($N_A - N_D$) based on absorption peaks (2802, 2454, and 1290 cm-1).
- SIMS (Secondary Ion Mass Spectrometry): Used for comparison to measure the complete boron concentration ($N_{imp}$).
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Charge Carrier Characterization (Dynamic):
- Admittance Spectroscopy (AS): The primary non-destructive method used to measure the dynamic characteristics of charge carriers and impurity centers, scanning temperature (15-475 K) and frequency (100 Hz-2 MHz).
- Capacitance-Voltage (C-V) Profiling: Used to determine the concentration of ionized impurity ($N_A - N_D$) and free charge carriers ($p_{CV}$) by differentiating the $C-V$ characteristics, particularly at low frequencies and high temperatures to approach quasi-static conditions.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the high-quality, custom Boron-Doped Diamond materials required to replicate, extend, and commercialize the research presented in this paper. Our MPCVD capabilities ensure precise control over doping, thickness, and surface quality, addressing the critical material requirements for advanced diamond semiconductor devices.
Applicable Materials
Section titled “Applicable Materials”To replicate the high-performance BDD SCD structures characterized in this study, 6CCVD recommends the following materials from our catalog:
- Boron-Doped Single Crystal Diamond (BDD SCD):
- For Epitaxial Layers: We offer BDD SCD films with thicknesses ranging from 0.1 µm up to 500 µm, grown on high-quality HPHT (100) or (111) substrates, allowing researchers to precisely control the doping profile ($N_A$ up to $10^{20}$ cm-3) necessary to achieve the desired activation energy reduction (e.g., 100 meV).
- For Bulk Studies: SCD Substrates up to 10 mm thick are available for bulk characterization and high-power device fabrication.
- Polycrystalline Diamond (PCD):
- For large-area applications (e.g., biosensors or heat spreaders) requiring high thermal conductivity and wide electrochemical windows, we offer Boron-Doped PCD (BDD PCD) plates up to 125 mm in diameter.
Customization Potential
Section titled “Customization Potential”The research highlights the necessity of precise dimensions, specific crystal orientations, and high-quality metal contacts. 6CCVD provides comprehensive customization services to meet these exact engineering requirements:
| Research Requirement | 6CCVD Customization Capability | Value Proposition |
|---|---|---|
| Specific Dimensions | Plates/wafers up to 125 mm (PCD) and custom SCD sizes. | We can supply the 3x3 mm to 5x5 mm samples used, or scale up to larger inch-size wafers for commercial production runs. |
| Layer Thickness | SCD/PCD thickness control from 0.1 µm to 500 µm. | Precise control over epitaxial layer thickness (e.g., 2.0-2.7 µm) is guaranteed for optimal device design and doping profile management. |
| Metal Contacts (Pt) | Internal metalization capability: Au, Pt, Pd, Ti, W, Cu. | We can deposit the required Platinum (Pt) Schottky contacts, or complex multi-layer stacks (e.g., Ti/Pt/Au) directly onto the diamond surface, streamlining the fabrication process. |
| Surface Quality | Polishing to Ra < 1 nm (SCD) and Ra < 5 nm (PCD). | Our ultra-low roughness polishing exceeds the 1-3 nm Ra achieved in the paper, ensuring superior interface quality for electrical contacts and minimizing surface defects. |
Engineering Support
Section titled “Engineering Support”The paper emphasizes the complexity of interpreting C-V and Admittance Spectroscopy data in diamond due to incomplete ionization and frequency dispersion. 6CCVD offers specialized support to overcome these challenges:
- Expert Consultation: 6CCVD’s in-house PhD material science team provides engineering support for material selection, doping optimization, and interpretation of electrophysical diagnostics for similar high-voltage electronics and wide bandgap semiconductor projects.
- Process Optimization: We assist clients in defining optimal growth parameters (e.g., B/C ratio, substrate temperature) to achieve specific target activation energies ($E_A$) and charge carrier concentrations ($p$) required for functional devices.
- Global Logistics: We ensure reliable global shipping (DDU default, DDP available) for sensitive diamond materials and finished components.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A critical analysis of the existing methods of controlling the concentration of impurity and majority charge carriers in wide bandgap semiconductors and the issues of improvement of modern diagnostics of the main electrophysical properties of single-crystal diamond are considered based on the results of our studies and the works of other authors. It was found that independent assessment of impurity concentration and concentration of free charge carriers is of fundamental importance for semiconductor diamond due to very low (less than 1%) degree of ionization of the introduced impurity. The advantages and prospects of admittance spectroscopy as a diagnostic method for ultrawide bandgap semiconductors are shown and solutions aimed at the correct interpretation of the experimental data are proposed. The high ionization energy of boron impurity in diamond (370 meV) results in a strong frequency dispersion of the measured barrier capacitance. It is shown that under disturbance of quasi-static conditions in capacitance-voltage measurements, low frequencies and high temperatures should be used for correct assessment of the charge carrier concentration. The results of electrophysical studies are compared with traditional measurements of impurity concentration in diamond by optical methods. A decrease of hole activation energy from the boron impurity level from 325 to 100 meV was found upon increasing the boron concentration NA from 2·10 16 to 4·10 19 cm -3 . The transition to the hopping mechanism of conductivity within the impurity (acceptor) band with thermal activation energy of 10-20 meV was registered for N A ≥5·10 18 cm -3 at temperatures of 120-150 K. Keywords: single-crystal diamond, boron impurity, charge carrier concentration, activation energy, admittance spectroscopy, capacitance-voltage measurements.