Physical modeling and design of a non-volatile optically gated high-power diamond transistor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-08-19 |
| Authors | S. Nandi, E. J. White, Qinghui Shao, Clint D. Frye, Mohamadali Malakoutian |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Innovation (DOGFET): The Diamond Optically Gated Field-Effect Transistor (DOGFET) is a high-power, diamond-based JFET utilizing both electrical (back gate) and low-power optical (530 nm laser) control.
- Non-Volatile Operation: The device exhibits a âlock-on/memoryâ effect, retaining its ON or OFF state for extended periods (minutes) when the optical gate is removed, functioning as a non-volatile 1T memory element.
- High Power Performance: The planar device achieves a high breakdown voltage (VBD >1850 V) and a high current density (1750 A/cm2), leveraging diamondâs exceptional critical electric field (~11 MV/cm).
- Low Optical Power Requirement: Efficient switching is achieved with laser intensities as low as 10 W/cm2, which is several orders of magnitude lower than typical Photoconductive Semiconductor Switches (PCSS).
- Gating Mechanism: Optical excitation (530 nm) activates deep nitrogen donor traps (1.7 eV) in the Type Ib substrate, increasing substrate conductivity and enabling the back gate to modulate the channel depletion region.
- Future Scaling: While the planar structure is limited to kHz switching speeds, predictive modeling is guiding the development of FinFET and Gate-All-Around (GAA-FET) structures targeting MHz switching frequencies.
- Modeling Framework: A key technical achievement is the development of a Physical Model Interface (PMI) coupled with the Sentaurus TCAD solver to accurately model the unique sub-gap trap excitation physics.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Device Type | JFET | N/A | Diamond Optically Gated Field-Effect Transistor (DOGFET) |
| Substrate Material | Type Ib Diamond | N/A | Contains Nitrogen deep traps |
| Epi-layer Thickness (Optimal) | 400 | nm | Boron-doped channel layer |
| Epi-layer B-Doping (Optimal) | 1017 | cm-3 | Channel doping concentration |
| Nitrogen Trap Energy | 1.7 | eV | Activation energy below conduction band |
| Breakdown Voltage (VBD) | >1850 | V | Planar device simulation result |
| Critical Field (Ecrit) | ~11 | MV/cm | Peak electric field concentration |
| Drain Current Density | 1750 | A/cm2 | For 400 nm channel thickness |
| Switching Frequency (Planar) | >2 | kHz | Achieved with 5 ”m channel length |
| Laser Wavelength (λ) | 530 | nm | Used for sub-gap excitation |
| Minimum Laser Intensity | 10 | W/cm2 | Required for efficient optical gating |
| Diamond Bandgap | 5.5 | eV | Ultra-wide bandgap |
| Thermal Conductivity | ~2200 | W/mK | Highest known material property |
| Hole Mobility (Channel) | 1193 | cm2/Vs | Low-field mobility in B-doped diamond |
Key Methodologies
Section titled âKey Methodologiesâ- Substrate Synthesis (HPHT): Type Ib diamond substrates were grown using the High-Pressure High-Temperature (HPHT) process (5-5.5 GPa, 1350-1450 °C). Substitutional nitrogen was introduced during growth, resulting in a deep donor concentration of 1018 cm-3.
- Epitaxial Layer Growth (CVD): A boron-doped p-type diamond epi-layer was grown on the Type Ib substrate via Chemical Vapor Deposition (CVD) at 200 Torr. The gas mixture included H2, CH4, and Trimethyl Borate (TMB) as the boron precursor.
- Surface Termination: Oxygen termination was used to create a p-type surface for the channel, while hydrogen termination was used to replicate p+ ohmic contacts (1019 cm-3 equivalent concentration).
- Device Simulation (TCAD): The DOGFET was modeled in 2D using the Synopsys Sentaurus TCAD solver, employing an axis-aligned Delaunay mesh optimized for high density at interfaces.
- Physical Model Interface (PMI): A user-defined PMI was implemented to integrate the physics of sub-gap trap excitation (emission and capture of carriers from deep nitrogen traps) directly into the electrical transport solver, ensuring a self-consistent solution.
- Transport Modeling: Device simulation self-consistently solved the Poisson and drift-diffusion equations. Low-field mobility was modeled using the Masetti model, and high-field transport was modeled using the Canali mobility model.
- Breakdown Analysis: Avalanche breakdown was modeled using the van Overstraeten-de Man Model (derived from the Chynoweth law), utilizing two different coefficient sets (Hiraiwa and Kamakura) to predict the high breakdown voltage.
Commercial Applications
Section titled âCommercial Applicationsâ- High-Power Grid Control: Utilizing the high breakdown voltage (>1850 V) and high current density (1750 A/cm2) for efficient power conversion and management in electrical grids.
- EMI/RF Immune Systems: The optical gating mechanism makes the device immune to electromagnetic interference, suitable for use in high-EMI environments and sensitive RF ICs.
- Advanced Power Conversion: Applications in high-power, high-frequency switching devices, such as those required for electric vehicles and large-scale data centers, leveraging diamondâs superior thermal management (2200 W/mK).
- Non-Volatile Memory (NVM): The âlock-on/memoryâ effect allows the DOGFET to function as a low-power, single-transistor (1T) memory cell, reducing the required duty cycle of the gate signal.
- Quantum Technology (Future): The developed PMI simulation framework is directly transferable to modeling particle excitation in deep-defect based quantum systems, such as color centers (NV centers) in diamond and SiC, for quantum computing and sensing applications.