Growth of synthetic diamond films and their electrophysical properties
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-12-26 |
| Journal | UNEC journal of engineering and applied sciences |
| Authors | Asef Nabiyev, J. I. Huseynov |
| Institutions | Azerbaijan State Pedagogical University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the growth and precise doping of synthetic diamond films via Chemical Vapor Deposition (CVD) for advanced semiconductor applications, focusing on achieving high-performance p-type conductivity and device fabrication.
- High-Quality Material: Optimal CVD conditions were established to grow high-perfection, single-crystal homoepitaxial diamond structures suitable for wide-temperature-range semiconductor devices.
- Precise Doping Control: Boron ion implantation (B+) was successfully used to create controllable p-type conductive layers. Varying implantation energy (10 keV to 350 keV) allowed for the formation of either near-surface conducting layers or deeply buried conducting layers (up to 1.2 ”m depth).
- High Hole Mobility: The implanted and annealed diamond exhibited excellent electrical properties, achieving low boron activation energies (Ea = 0.03 eV at low temperatures) and high hole mobility (up to 520 cm2/(V·s) measured).
- Simplified H-Termination: Thermal annealing in a hydrogen atmosphere (800-1000°C) was validated as a simpler and more reproducible alternative to conventional microwave plasma treatment for forming the necessary p-type conductive hydrogenated surface layer.
- Device Demonstration: A field-effect transistor (FET) was successfully fabricated on a hydrogenated diamond surface, demonstrating key transistor properties, including current modulation, channel overlap, saturation, and low gate leakage at a maximum gate voltage of 5 V.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| CVD Gas Mixture | 2% CH4 - 98% H2 | % | Gas composition for diamond growth |
| CVD Residual Pressure | ~0.27 | Pa | During film deposition |
| Optimal Substrate Temperature | ~900 | °C | For cubic diamond structure formation |
| Film Growth Rate (CVD) | 1-2 | ”m/h | Rate achieved by the given method |
| Boron Implantation Dose | 3x1015 to 5x1015 | cm-2 | Range used for creating conductive layers |
| Boron Implantation Energy (Buried Layer) | 350 | keV | Creates buried layer ~100 nm thick |
| Post-Implantation Annealing T | 1380-1500 | °C | Required for lattice recovery and boron activation |
| Hole Mobility (Measured Max) | 520 | cm2/(V·s) | Achieved in sample with high N concentration |
| Boron Activation Energy (Low T) | 0.03 | eV | Observed at low temperatures (shallow centers) |
| Boron Activation Energy (High T) | 0.07 | eV | Observed at high temperatures (deeper centers) |
| H-Termination Annealing T | 800-1000 | °C | Thermal treatment in H2 flow (30 min) |
| FET Gate Length (L) | 35 | ”m | Manufactured sample dimension |
| FET Gate Width (W) | 1 | mm | Manufactured sample dimension |
| FET Max Gate Voltage | 5 | V | Demonstrated operating voltage |
| Diamond Resistivity (Intrinsic) | 1012 - 1013 | Ω·cm | Used as the gate dielectric |
| Dielectric Intensity (Calculated) | 30 | MV/cm | Intensity in dielectric barrier at U=5V |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized Microwave Plasma Chemical Vapor Deposition (MPCVD) combined with ion implantation and thermal processing to synthesize and dope the diamond films.
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Diamond Film Growth (CVD):
- Films were deposited on single-crystal silicon substrates (KDB-12, /100/ orientation).
- A gas mixture of 2% CH4 and 98% H2 was decomposed in a microwave plasma discharge (2.45 GHz, 200-300 W power).
- Substrate temperature was maintained near 900°C under a residual pressure of ~0.27 Pa.
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Boron Doping:
- Boron ions (B+) were implanted using an ion accelerator.
- Near-Surface Doping: Low energies (10-25 keV) were used, often employing an Aluminum (Al) mask (30-80 nm thick) to control the projective range and maximize concentration near the surface (12-20 nm depth).
- Buried Layer Doping: High energies (e.g., 350 keV) were used to create buried conducting layers approximately 100 nm thick.
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Post-Implantation Processing:
- Samples underwent high-temperature post-implantation annealing (1380°C to 1500°C) to repair lattice damage (amorphization/graphitization) and electrically activate the implanted boron atoms.
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Hydrogen Surface Termination (H-Layer):
- To form the p-type conductive surface layer, crystals were annealed in a hydrogen atmosphere at atmospheric pressure, typically at 900°C for 20 minutes. This thermal method was shown to be a reproducible alternative to plasma treatment.
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Device Fabrication (FET):
- A non-conducting diamond layer (~200 nm) served as the dielectric for the MIS structure.
- Copper (Cu) was deposited (60 nm thick) via resistive evaporation to form the gate, source, and drain contacts.
- Photolithography and air plasma etching (0.4 Torr) were used to define the active zone and eliminate the hydrogen surface on open sections, ensuring low gate leakage.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to grow high-quality, doped diamond films with controlled conductivity profiles is critical for next-generation electronic devices operating under extreme conditions.
- High Power RF Devices: Diamondâs high breakdown voltage and thermal conductivity enable the development of high-power, high-frequency transistors (e.g., MISFETs) and switches that surpass silicon and silicon carbide limits.
- Thermal Management Systems: Utilizing the record thermal conductivity of synthetic diamond films for efficient heat abstraction in densely integrated microelectronics, such as high-current and high-voltage modules.
- Harsh Environment Electronics: The chemical inertness, high temperature resistance (up to 700 K tested), and radiation hardness of diamond make these devices suitable for aerospace, defense, and industrial monitoring applications.
- Nonvolatile Memory Elements: Diamond films can serve as robust, high-quality dielectric layers in Metal-Dielectric-Semiconductor (MDS) structures for nonvolatile memory.
- Two-Dimensional Material Integration: The use of diamond as a substrate or dielectric for emerging 2D materials (like graphene) in nanoelectronics, leveraging its insulating properties and stability.
View Original Abstract
The possibilities of formation of single-crystal homoepitaxial diamond structures grown by the method of vapor-phase chemical deposition are investigated. Optimal technological conditions for the formation of structures are suggested. The layer with p-type conductivity formation process depending on the temperature and time is determined. It was shown that applied thermal treatment method in hydrogen can be an alternative to the conventional method of H layer formation in microwave hydrogen plasma due to simpler and more reproducible. The profile distribution of boron atoms in a diamond crystal was determined under different implantation modes. The temperature dependence of specific conductivity in the temperature range 80-700 K was studied, and the activation energy was calculated. The results of Hall measurements of the electrophysical parameters of implanted samples are presented, and the effect of nitrogen concentration on the electrophysical parameters is revealed. The electrophysical parameters of the structures obtained under various modes of ion implantation of boron in a crystal and subsequent annealing are presented. The possibility of creating a field effect transistor on a hydrogenated diamond surface is shown. The current-voltage characteristic of the manufactured sample was studied and it was shown that it demonstrates low leakage through the gate.