High-mobility p-channel wide-bandgap transistors based on hydrogen-terminated diamond/hexagonal boron nitride heterostructures
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-23 |
| Journal | Nature Electronics |
| Authors | Yosuke Sasama, Taisuke Kageura, Masataka Imura, Kenji Watanabe, Takashi Taniguchi |
| Institutions | National Institute for Materials Science, University of Tsukuba |
| Citations | 154 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research reports the fabrication of high-performance, normally-off p-channel wide-bandgap field-effect transistors (FETs) utilizing hydrogen-terminated diamond (H-diamond) and hexagonal boron nitride (h-BN) heterostructures.
- Mobility Breakthrough: Achieved the highest room-temperature Hall hole mobility (680 cm2V-1s-1) reported for any p-channel wide-bandgap semiconductor FET, surpassing GaN and SiC counterparts.
- Normally-Off Operation: Successfully demonstrated normally-off behavior (Vth = -0.99 V) with a high on/off ratio exceeding 108, crucial for fail-safe power electronics.
- Record On-State Performance: Achieved the lowest sheet resistance (1.4 kΩ) and highest gate-length-normalized on-current (1600 ”m mA mm-1) for p-channel wide-bandgap FETs.
- Novel Mechanism: Conductivity is generated by an inversion layer of holes induced by gate bias, eliminating the need for traditional surface transfer doping (STD) which relies on ionized surface acceptors.
- Reduced Scattering: The air-free fabrication process significantly reduces atmospheric surface acceptors, minimizing carrier scattering and enabling the high mobility observed.
- Cryogenic Stability: Gate controllability and high mobility are retained down to cryogenic temperatures (4.5 K), suggesting suitability for extreme environments.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Room-Temperature Hall Mobility (”Hall) | 680 | cm2V-1s-1 | Highest reported for p-channel wide-bandgap FETs (Device C1) |
| Low-Temperature Mobility | >1000 | cm2V-1s-1 | Measured at 150 K (VGS = -8 V) |
| Minimum Sheet Resistance (Ïmin) | 1.4 | kΩ | At VGS = -10 V (Device C1) |
| Maximum Normalized On-Current (LGIDmax/WG) | 1600 | ”m mA mm-1 | Highest reported for p-channel wide-bandgap FETs |
| On/Off Ratio | >108 | - | Measured at VDS = -10 V |
| Threshold Voltage (Vth) | -0.99 | V | Confirms normally-off (enhancement) mode operation |
| Maximum Hall Carrier Density (pHall) | 6.6 x 1012 | cm-2 | At VGS = -10 V |
| Minimum Subthreshold Swing (SS) | 130 | mV dec-1 | At VGS = -0.55 V |
| Interface Trap Density (Dit) | 6.8 x 1011 | cm-2eV-1 | Calculated from SS |
| Gate Leak Current Density | 3 x 10-7 | A cm-2 | Normalized by gate area (VGS = 0 to -10 V) |
| Gate-Source Breakdown Field | >4.2 | MV/cm | Based on 10 V applied across 24 nm h-BN |
| h-BN Gate Insulator Thickness (thBN) | 24 | nm | For devices C1 and C2 |
| Diamond Orientation | (111) | - | IIa-type single-crystalline diamond |
| Intrinsic Bulk Diamond Mobility (Phonon-limited) | >2000 | cm2V-1s-1 | Room temperature (Theoretical reference) |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication relies on an air-free transfer and lamination process to minimize atmospheric surface acceptors, which typically cause hole scattering and normally-on behavior in H-diamond FETs.
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Substrate Preparation:
- Used IIa-type (111) single-crystalline diamond.
- Surfaces were polished and cleaned using hydrofluoric acid and a mixture of sulfuric and nitric acid (200 °C).
- Ti/Pt Hall-bar electrodes were deposited via electron-beam lithography.
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Hydrogenation and Ohmic Contact Formation:
- Diamond was annealed in H2 gas (650 °C) and exposed to hydrogen plasma (600 °C, 10-12 min) in a CVD chamber.
- A second hydrogenation step (600-670 °C, 10 min) was performed in a separate CVD chamber.
- These steps formed TiC ohmic contacts and hydrogenated the diamond surface.
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Air-Free Transfer and Lamination (Critical Step):
- The H-diamond was transferred directly from the CVD chamber to an Ar-filled glove box using a custom-made vacuum suitcase (pressure < 10-7 Torr for Device C1).
- Single-crystalline h-BN (24 nm thick) was cleaved in the glove box and laminated onto the H-diamond using a dry transfer technique (completed within 3 hours of diamond transfer).
- The sample was annealed at 300 °C in Ar for 3 hours after h-BN lamination.
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Gate Electrode Deposition:
- A thin graphite crystal (Kish graphite) was transferred onto the h-BN in the glove box, followed by annealing at 300 °C for 1 hour.
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Device Patterning and Isolation:
- Graphite and h-BN were etched into a Hall-bar shape using plasma generated from N2, O2, and CHF3 gases (total pressure 10 Pa).
- The etching process converted the exposed H-diamond surface (outside the h-BN region) into an oxygen-terminated surface, providing electrical isolation.
- Ti/Au leads and bonding pads were deposited.
Commercial Applications
Section titled âCommercial ApplicationsâThe exceptional performance metrics achieved by this h-BN/diamond p-channel FETâspecifically the high mobility, normally-off operation, and low sheet resistanceâmake diamond a highly competitive material for next-generation wide-bandgap electronics.
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Power Electronics:
- Low-Loss Switching: The normally-off behavior and extremely low sheet resistance (1.4 kΩ) are ideal for high-efficiency power conversion systems, reducing conduction loss and cooling requirements.
- High-Temperature Operation: Diamondâs wide bandgap (5.47 eV) and high thermal conductivity (>2200 W m-1K-1) enable operation in harsh, high-temperature environments where SiC and GaN struggle.
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High-Frequency and RF Applications:
- The high hole mobility supports high-frequency operation, suitable for RF power amplifiers and high-speed switching devices.
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Complementary Circuits (CMOS):
- The development of a high-performance p-channel diamond FET paves the way for energy-efficient complementary circuits (CMOS) integrating p-channel diamond FETs with high-performance n-channel GaN FETs. This integration is crucial for low power consumption logic and driving circuitry.
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Extreme Environment Electronics:
- The retention of gate controllability and high mobility at cryogenic temperatures (down to 4.5 K) makes this technology viable for applications in outer space or specialized scientific instrumentation.
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Diamond Material Technology (6ccvd.com relevance):
- The reliance on high-quality, single-crystalline IIa-type (111) diamond substrates highlights the necessity of advanced CVD growth techniques for producing high-purity, low-defect materials essential for channel layers.