Transport Properties of the Two-Dimensional Hole Gas for H-Terminated Diamond with an Al2O3 Passivation Layer
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-03-14 |
| Journal | Crystals |
| Authors | Cui Yu, Chuangjie Zhou, Jianchao Guo, Zezhao He, Mengyu Ma |
| Institutions | Hebei Semiconductor Research Institute, Xiâan Jiaotong University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the carrier transport properties and scattering mechanisms of the Two-Dimensional Hole Gas (2DHG) in H-terminated diamond, focusing specifically on the impact of high-temperature Al2O3 passivation layers deposited via Atomic Layer Deposition (ALD).
- Performance Limitation: The primary factors limiting the performance of H-terminated diamond Field Effect Transistors (FETs) are high sheet resistance (Rs) and low carrier mobility (typically less than 200 cm2/(V·s)).
- Dominant Scattering Sources: Mobility fitting across the 90 K to 300 K range confirmed that Ionic Impurity (IM) scattering and Surface Roughness (SR) scattering are the dominant mechanisms limiting 2DHG transport.
- ALD Temperature Dependence: The resulting sheet density (Ns) after Al2O3 deposition is highly dependent on the ALD temperature. Ns decreased at 300 °C but increased at 450 °C, attributed to changes in the Al2O3 electron affinity and surface adsorbate desorption.
- Mobility Degradation: High-temperature ALD processes (400 °C and 450 °C) caused a decrease in carrier mobility, primarily due to the enhancement of Ionic Impurity scattering.
- Mechanism Insight: The high-temperature process desorbs surface adsorbates, and the ALD Al2O3 acts as a new transfer doping layer. The resulting negative fixed charges at the Al2O3/H-diamond interface increase the concentration of ionized impurities (NI).
- Design Implication: Optimizing the initial stage and deposition temperature of the ALD Al2O3 process is critical for reducing unoccupied levels in the dielectric and improving 2DHG carrier mobility.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Typical 2DHG Sheet Density (Ns) | 1012 to 1013 | cm-2 | H-terminated diamond |
| Typical Carrier Mobility (Ό) | < 200 | cm2/(V·s) | H-terminated diamond |
| ALD Deposition Temperatures | 300, 400, 450 | °C | Al2O3 passivation process |
| Measurement Temperature Range | 90 to 300 | K | Van der Pauw-Hall characterization |
| SC-Epitaxial Growth Temperature | 900 | °C | MPCVD process |
| H2 Plasma Treatment Temperature | 800 | °C | MPCVD process |
| Diamond Debye Temperature | ~2240 | K | Relevant for Optical Phonon scattering model |
| Acoustic Deformation Potential (Dac) | 8 | eV | Used for AC scattering fitting |
| Sample A (450 °C ALD) Mobility Change | 152 to 137 | cm2/(V·s) | Mobility decreased 9.9% after ALD |
| Sample C (300 °C ALD) Ns Change | 7.512 to 5.37 | 1012/cm2 | Ns decreased 28.6% after ALD |
| H-Diamond FET Benchmark (IDSmax) | 1.3 | A/mm | State-of-the-art DC performance |
| H-Diamond FET Benchmark (fmax) | 120 | GHz | State-of-the-art RF performance |
Key Methodologies
Section titled âKey Methodologiesâ- Diamond Sample Preparation: Three types of H-terminated diamond samples were prepared using Microwave Plasma CVD (MPCVD):
- SC-Epitaxial H-termination: Single crystal diamond grown homoepitaxially at 900 °C, 100 Torr pressure, 1 kW power, and 1% CH4/H2 ratio (500 sccm total flow).
- SC-H Plasma Treatment: Single crystal diamond treated in H2 plasma.
- PC-H Plasma Treatment: Polycrystalline diamond (grain size ~100 ”m) treated in H2 plasma.
- Hydrogen Plasma Treatment Parameters: Performed at 800 °C and 5 kPa chamber pressure for 40 minutes.
- Passivation Layer Deposition: Al2O3 films were deposited on single crystal samples (A, B, C) using Atomic Layer Deposition (ALD) at high temperatures (450 °C, 400 °C, and 300 °C, respectively).
- Electrical Characterization: Sheet resistance (Rs), sheet density (Ns), and carrier mobility (Ό) were measured using the Van der Pauw-Hall method.
- Temperature Dependence Study: Hall measurements were conducted in a low-temperature system across the range of 90 K to 300 K.
- Mobility Modeling: The temperature dependence of the 2DHG mobility was fitted using the Mathiessen rule, incorporating four distinct scattering mechanisms:
- Ionic Impurity (IM) scattering.
- Acoustic Phonon (AC) scattering.
- Optical Phonon (OP) scattering.
- Surface Roughness (SR) scattering.
Commercial Applications
Section titled âCommercial ApplicationsâThe optimization of 2DHG transport properties in H-terminated diamond is essential for realizing next-generation devices in several high-performance sectors:
- High Power Electronics: Diamondâs high critical breakdown electric field makes it ideal for high-voltage switching devices, power converters, and inverters, where low Rs is critical for efficiency.
- Radio Frequency (RF) Amplifiers: Achieving high carrier mobility and low parasitic resistance is necessary for maximizing the maximum oscillation frequency (fmax) and output power density in RF FETs used in communication systems.
- 5G and 6G Infrastructure: Diamond FETs are candidates for high-frequency (GHz range) power amplifiers required for advanced wireless communication base stations.
- High-Temperature Operation: Diamondâs superior thermal conductivity and wide bandgap allow devices to operate reliably in extreme environments where silicon or GaAs devices fail.
- Aerospace and Defense: Applications requiring radiation-hardened, high-power, and high-frequency components benefit from optimized diamond semiconductor technology.
View Original Abstract
Diamonds are thought to be excellent candidates of next-generation semiconductor materials for high power and high frequency devices. A two-dimensional hole gas in a hydrogen-terminated diamond shows promising properties for microwave power devices. However, high sheet resistance and low carrier mobility are still limiting factors for the performance improvement of hydrogen-terminated diamond field effect transistors. In this work, the carrier scattering mechanisms of a two-dimensional hole gas in a hydrogen-terminated diamond are studied. Surface roughness scattering and ionic impurity scattering are found to be the dominant scattering sources. Impurity scattering enhancement was found for the samples after a high-temperature Al2O3 deposition process. This work gives some insight into the carrier transport of hydrogen-terminated diamonds and should be helpful for the development of diamond field effect transistors.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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