Rapid Growth of Single Crystal Diamond at High Energy Density by Plasma Focusing
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Journal of Inorganic Materials |
| Authors | Yicun LI, Xuedong LIU, Xiaobin Hao, Bing Dai, Jilei Lyu |
| Institutions | Harbin Institute of Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the design and implementation of a specialized plasma focusing structure within a Microwave Plasma Chemical Vapor Deposition (MPCVD) reactor to achieve rapid growth of single-crystal diamond (SCD).
- Core Innovation: A conical plasma focusing structure, optimized via Magnetohydrodynamic (MHD) simulation, was designed to concentrate plasma energy density (PED) under conventional operating conditions (3500 W, 18 kPa).
- Performance Achievement: The maximum SCD growth rate reached 97.5 ”m/h (Sample S4), representing a 10-fold increase over the baseline molybdenum disk setup (9.5 ”m/h, Sample S1).
- Energy Density: The focusing structure achieved a PED of 793.7 W/cm3, which is 3.9 times higher than the conventional setup (205.4 W/cm3).
- Simulation Validation: MHD modeling predicted that the core electric field and electron density would increase by approximately 3 times using the focusing structure, a result consistent with experimental observations of Hα intensity.
- Process Optimization: The highest growth rate was achieved through the combined use of the focusing structure and the addition of 300 ppm nitrogen (N2), which significantly enhances growth kinetics but introduces NV color centers.
- Key Advantage: This method achieves high PED and rapid growth without resorting to extremely high pressures (e.g., >40 kPa), thus mitigating plasma instability issues common in high-pressure MPCVD.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Growth Rate (S4) | 97.5 | ”m/h | Focusing structure + 300 ppm N2 |
| Baseline Growth Rate (S1) | 9.5 | ”m/h | Mo disk, 0 ppm N2 |
| Plasma Energy Density (Focusing) | 793.7 | W/cm3 | 3.9x increase over baseline |
| Plasma Energy Density (Mo Disk) | 205.4 | W/cm3 | Conventional setup |
| Microwave Power | 3500 | W | All experiments |
| Growth Pressure | 18 | kPa | All experiments (Sub-atmospheric) |
| Core E-Field Increase (Simulated) | ~3 | times | Focusing structure vs. Mo disk |
| Electron Density Increase (Simulated) | ~3 | times | Focusing structure vs. Mo disk |
| Growth Temperature | 900 | °C | Controlled via substrate height |
| CH4 Concentration | 5 | % | 10 sccm CH4 / 190 sccm H2 |
| N2 Concentration (High Rate) | 300 | ppm | 0.06 sccm N2 |
| Diamond Raman Peak (S4) | 1331.6 | cm-1 | Shifted from ideal 1332.5 cm-1 due to N2 doping |
| Focusing Structure Height | 20.91 | mm | Optimized conical geometry |
Key Methodologies
Section titled âKey MethodologiesâThe rapid growth of SCD was achieved through a combination of simulation-driven design and optimized process parameters:
- Reactor Design and Simulation:
- A special conical plasma focusing structure was designed and optimized using Magnetohydrodynamic (MHD) modeling (COMSOL software).
- The structure was integrated into the MPCVD reactor as a metal boundary condition to maximize core electric field and electron density.
- Substrate and Temperature Control:
- Substrates were 5 mm x 5 mm x 0.5 mm, (100)-oriented CVD SCD seeds (optical grade).
- Growth temperature was maintained at 900 °C using an infrared thermometer (IR-AH, CHINO) by adjusting the height of the water-cooled substrate stage.
- Gas Recipe and Process Conditions:
- The primary source gases were high-purity H2 (190 sccm) and CH4 (10 sccm, 5%).
- Experiments were conducted at a fixed microwave power of 3500 W and a pressure of 18 kPa.
- Nitrogen (N2) was intentionally added at 300 ppm (0.06 sccm) for high-rate growth experiments (S3, S4).
- Plasma Characterization:
- Plasma properties were monitored using Optical Emission Spectroscopy (OES, Maya2000) to track Hα (656 nm) and CN (388 nm) intensities, indicating the concentration of key growth species.
- Plasma imaging (Zyla 5.5 camera with Hα filter) was used to visually confirm plasma focusing and accurately calculate the effective plasma volume (Va) for determining PED.
- Sample Analysis:
- Growth rate was determined by measuring the thickness difference before and after the 10-hour growth period using a micrometer.
- Crystal quality and morphology were assessed using optical microscopy (WMP-6880) and Raman spectroscopy (LabRAM HR Evolution, 532 nm laser).
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to rapidly synthesize high-quality SCD under stable, moderate-pressure conditions significantly lowers production costs and expands the viability of diamond in several advanced technological sectors:
- High-Power Electronics and Thermal Management: SCDâs superior thermal conductivity (2000 W/(m·K)) makes it an ideal heat spreader for high-frequency and high-power devices (e.g., 5G/6G communication modules, electric vehicle fast charging infrastructure).
- Quantum Technology: Controlled nitrogen doping (as demonstrated in S4) creates NV color centers, which are crucial for developing room-temperature quantum sensors, quantum computing components, and solid-state lasers (Raman lasers).
- Semiconductor Devices: SCD is considered the âultimate semiconductorâ due to its wide bandgap. Rapid growth enables the cost-effective production of electronic-grade diamond for high-voltage power devices and deep-space radiation detectors.
- Optical Windows and Lenses: The high purity and large size achievable through high-rate growth are essential for producing robust optical components used in high-power laser systems.
- Advanced Detectors: SCD is used in alpha-voltaic batteries and UV detectors, benefiting from the ability to grow thicker, high-quality epitaxial layers quickly.
View Original Abstract
Single crystal diamond is a kind of crystal material with excellent performance, which has important application value in advanced scientific field.In the field of single crystal diamond growth by microwave plasma chemical vapor deposition (MPCVD), improvement of crystal growth rate is still a key challenge, although corrent high energy density plasma has been a ralatively effective method.In this work, a special plasma focusing structure was designed through magnetohydrodynamic (MHD) model simulation which then was used in the growth experiment