ELECTRON IRRADIATION OF AN UNDOPED HOMOEPITAXIAL DIAMOND TO SUPPRESS HOLE CONDUCTIVITY
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-06-20 |
| Journal | IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA |
| Authors | Vera O. Timoshenko, D. D. Prikhodko, С. А. Тарелкин, S. I. Zholudev, Nikolay V. Luparev |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates a highly effective method for suppressing background hole conductivity in undoped homoepitaxial Chemical Vapor Deposition (CVD) diamond using low-dose, high-energy electron irradiation.
- Core Problem Solved: Residual boron (B) impurities (concentration < 1014 cm-3) caused high background conductivity (~5 kΩ·cm), resulting in excessive dark current (> 100 µA) in detector structures, rendering them unusable.
- Mechanism: Irradiation with 3.5 MeV electrons creates deep vacancy-related centers that electrically compensate the shallow boron acceptors, effectively eliminating the p-type conductivity.
- Performance Improvement: The material resistivity increased by approximately six orders of magnitude at room temperature, exceeding the 10 GΩ·cm measurement limit.
- Detector Dark Current: Dark current in the fabricated detectors dropped dramatically from the measurement limit (> 100 µA) to less than 1 nA across a ±600 V range post-irradiation.
- Enhanced Stability: The suppression of conductivity is thermally stable up to 1000 K, allowing the use of robust, high-temperature annealed Ohmic contacts (Ti/Pt) instead of less stable Schottky contacts.
- Engineering Advantage: Irradiated samples with stable Ohmic contacts achieved dark current performance comparable to unirradiated samples using sensitive Schottky contacts, significantly improving mechanical and thermal reliability for extreme environments.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electron Irradiation Energy | 3.5 | MeV | Used to create compensating vacancies |
| Irradiation Dose (Low) | 2·1015 | cm-2 | Sample #1 |
| Irradiation Dose (High) | 1016 | cm-2 | Sample #2 |
| Initial Resistivity (RT) | ~5 - 6 | kΩ·cm | Unirradiated material |
| Final Resistivity (Sample #2, RT) | > 10 | GΩ·cm | Exceeded measurement threshold (300-1000 K) |
| Dark Current (Irradiated) | < 1 | nA | Measured at ±600 V (Ohmic contacts) |
| Dark Current (Unirradiated) | > 100 | µA | Exceeded measurement threshold (Schottky contacts) |
| Thermal Stability | Up to 1000 | K | Conductivity suppression maintained |
| Boron Impurity Concentration | < 1014 | cm-3 | Background concentration in starting material |
| Ohmic Contact Annealing Temp | 700 | °C | Ti/Pt contact stability |
| CVD Substrate Temperature | 850 ± 15 | °C | Material synthesis parameter |
| CVD Gas Ratio (H2/CH4) | 24/1 | Ratio | Material synthesis parameter |
Key Methodologies
Section titled “Key Methodologies”The study utilized undoped homoepitaxial diamond grown via CVD and characterized its electrophysical properties before and after high-energy electron irradiation.
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Material Growth:
- Diamond single crystals were grown using a Plassys BJS 150 CVD system.
- Growth parameters included a substrate temperature of 850 ± 15 °C, 2.7 kW microwave power, H2/CH4 ratio of 24/1, and a gas pressure of 180 ± 5 mbar.
- The resulting growth rate was approximately 1.5 - 2 µm/h.
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Sample Preparation and Irradiation:
- Three 4x4x0.5 mm square plates were prepared.
- Samples #1 and #2 were subjected to 3.5 MeV electron irradiation at doses of 2·1015 cm-2 and 1016 cm-2, respectively.
- Irradiation dose control was monitored by measuring the concentration of neutral vacancies (V0, or GR centers) formed.
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Contact Fabrication:
- Ohmic Contacts (Irradiated Samples): Standard technology involving magnetron sputtering of Titanium (Ti) and Platinum (Pt), followed by annealing at 700 °C.
- Schottky Contacts (Unirradiated Comparison Sample #3): Samples were annealed at 650 °C, surface treated with SF6 plasma for 20 minutes, and then contacts were deposited in a rounded rectangular geometry.
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Electrophysical Characterization:
- Resistivity and Hall Effect: Measured using the Van der Pauw method (LakeShore HMS 7707) across a temperature range of 300 K to 1000 K to confirm thermal stability and compensation mechanism.
- Detector Performance: Current-Voltage (I-V) characteristics were measured in a vertical (detector) geometry using a high-voltage source (Fug DC Power Supply) and a picoammeter (Keithley 6485) in the range of -600 V to +600 V.
Commercial Applications
Section titled “Commercial Applications”This technology directly supports the development of highly reliable diamond-based semiconductor devices, particularly those designed for operation in harsh environments.
- High-Energy Physics Detectors: Creation of robust detectors for high-energy particles (protons, neutrons, alpha, beta, gamma rays) used in accelerators and colliders.
- Radiation Dosimetry: Manufacturing stable, low-dark-current detectors for precise measurement of ionizing radiation, including X-rays and UV.
- Extreme Environment Electronics: Devices requiring high thermal and mechanical stability, enabled by the use of robust Ti/Pt Ohmic contacts (stable up to 1000 K) instead of conventional Schottky barriers.
- Nuclear and Space Applications: Diamond detectors resistant to high radiation doses and temperature cycling, crucial for monitoring and sensing in nuclear reactors or space missions.
- Self-Compensating Devices: Potential for “self-healing” detectors where residual conductivity is suppressed in situ by exposure to the operational ionizing radiation stream itself.
View Original Abstract
The use of undoped single-crystal diamond as material for the manufacture of detectors for high-energy particles and various types of ionizing radiation is limited by background conductivity caused by boron impurities, leading to high dark currents in such metal-semiconductor-metal or metal-dielectric-metal structures. This study explores the possibility of reducing background conductivity in undoped homoepitaxial diamond through irradiation with low doses of high-energy electrons (3,5 MeV). We studied single-crystal diamonds with impurity concentrations below 1014 cm-3 nevertheless demonstrating resistivity of ~5 kΩ∙cm at room temperature. The samples were irradiated with electron doses of ~2∙1015 cm-2 and ~1016 cm-2. The results were monitored by analyzing the temperature dependence of the material’s electrophysical properties and the current-voltage characteristics of detector samples made from it. The obtained results show that irradiation effectively reduces diamond conductivity by several orders of magnitude. Studies of the temperature dependences of electrophysical parameters confirm the material’s stability after irradiation in the temperature range up to 1000 K, enabling the fabrication of ohmic contacts in detector structures without degradation of their characteristics. Measurements of current-voltage characteristics demonstrate a significant reduction in the dark current of a detector after irradiation. Moreover, the dark current of the irradiated samples with ohmic contacts, which exhibit enhanced mechanical and thermal stability, is comparable to that of non-irradiated samples with Schottky contacts. The obtained data open prospects for developing homoepitaxial diamond-based detectors resistant to extreme operating conditions. For citation: Timoshenko V.O., Prikhodko D.D., Tarelkin S.A., Zholudev S.I., Luparev N.V., Kornilov N.V. Electron irradiation of an undoped homoepitaxial diamond to suppress hole conductivity. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 9. P. 53-59. DOI: 10.6060/ivkkt.20256809.12y.