What kind of semiconductor is r-GeO₂?
Basic Physical Properties Table for r-GeO₂
| Characteristics | r-GeO₂ |
|---|---|
| Bandgap (eV) | 4.45~4.77(Measured) |
| Breakdown field (MV/cm) | |
| Electron mobility (cm²/Vs)) | |
| Hole mobility (cm²/Vs) | |
| Thermal conductivity (W/m K) | |
| Average thermal expansion coefficient (/K) (Room temp. -600℃)((001) plane) | 3.9×10⁻⁶(Measured)* |
| Baliga’s Figure of Merit (Si=1) | |
| Vickers hardness (Hv) （(110) plane) | 1610 (Measured)* |
| Young’s modulus (GPa) | 293GPa(Measured)* |
(4.45-4.77 Patentix)
(The Bandgap value is 4.85-5.63 from literature).
*n=1.
The physical property values left blank are currently being measured. We will update them as soon as they are available for disclosure.
Features of r-GeO₂
Reducing energy losses during power conversion contributes to lowering CO₂ emissions and helps realize a sustainable low-carbon society.
Future Challenges for r-GeO₂ Semiconductors
・While both p-type and n-type are theoretically possible, experimental verification of p-type conduction remains a significant challenge.
・Currently, while n-type conduction has been reported, p-type conduction remains at the stage where electrical characteristics suggesting its possibility have been confirmed. Full verification of both polarities and the development of doping technology to stably realize and control them are necessary.
Improving Breakdown Voltage and Reliability
・Power semiconductors require high reliability to withstand electrical breakdown when controlling high voltages.
・r-GeO₂ possesses an extremely large bandgap (4.7 eV), suggesting high breakdown voltage potential. However, establishing techniques to suppress breakdown phenomena and prevent physical damage during actual device operation remains a challenge.
Film deposition technology and high-quality crystal growth ・To fabricate semiconductor devices, high-quality thin-film deposition technology and single-crystal growth technology with minimal defects are essential.
・For the new material r-GeO₂, it is essential to optimize a proprietary film deposition process suitable for mass production with stable quality and to ensure compatibility with substrate materials.
Device Structure Optimization and Evaluation
・After confirming the fundamental properties of the materials, it is necessary to design and fabricate device structures such as transistors and evaluate their electrical characteristics in detail.
・Establishing the optimal device structure and process technology to maximize its theoretical potential is key to practical implementation. By overcoming these challenges, r-GeO₂ is expected to be applied in fields such as power transmission and electric vehicles as the ultimate energy-saving device, surpassing existing wide-bandgap semiconductors like SiC and GaN.
Challenges in the Practical Application of r-GeO₂ Substrates
・A large-diameter substrate of at least 6 inches is required.
To enable power device manufacturers to produce power devices using r-GeO₂substrates, it is necessary to supply r-GeO₂ substrates sized to fit existing production equipment (6 inches or larger).
・The transition to 6-inch standalone substrates (bulk substrates) is difficult.
To achieve a 6-inch r-GeO₂ freestanding substrate, it is necessary to grow a single crystal ingot with a diameter of 100 mm or more. However, the single crystals currently being produced are only about 5 mm in diameter, meaning a long development period is required to realize a 6-inch substrate. Furthermore, due to the soaring price of the raw material (germanium), even if a 6-inch r-GeO₂ freestanding substrate were to be realized, it is anticipated that reducing the substrate price would be difficult.
GeO₂ on Si Substrates Suitable for Large-Area Fabrication and Low-Cost Production
If thin films of single-crystal r-GeO₂ can be heteroepitaxially grown on inexpensive Si substrates, the use of germanium dioxide raw materials can be significantly reduced. This enables the provision of next-generation semiconductor r-GeO₂ substrates at a lower cost than existing SiC substrates. Furthermore, by using conductive materials for the buffer layer—the key to achieving heteroepitaxial growth of r-GeO₂ single-crystal films on Si substrates—we aim to realize GeO₂ on Si substrates. This would facilitate the implementation of vertical device structures, a common configuration in power devices.
Half-inch r-GeO₂ Freestanding Substrate for Ultra-High-Performance Power Devices
r-GeO₂ freestanding substrates are being developed with the goal of achieving a half-inch (0.5-inch) size.
In addition to basic research applications at universities and research institutions, freestanding substrates aim for application in fields previously unattainable with conventional materials, such as ultra-high-voltage power devices and radiation-resistant power devices, due to their ability to achieve high crystal quality.
Expected applications
Electric vehicles (EV) / Railways
Improvements in power conversion efficiency contribute to extending the cruising range of EVs, shortening charging times, and making inverters smaller and lighter. This technology is also applied to railway vehicle power systems.
Renewable energy
It is used in power conditioners for solar and wind power generation, maximizing conversion efficiency and reducing transmission losses, thereby accelerating the spread of clean energy.
Industrial Equipment
Applied to motor control and power supply equipment within factories, it contributes to energy savings across the entire system.
Data Centers
Applied to server power supplies in data centers, it contributes to energy savings across the entire system.
Home appliances
Built into inverters for air conditioners, refrigerators, and other appliances, it significantly reduces power consumption. It supports the realization of more high-performance and environmentally friendly home appliances.
Various power supply devices
From smartphone chargers to industrial power supplies, we promote the optimization of energy use by achieving high efficiency and miniaturization in all power conversion devices.