Group IV Semiconductor Materials for Low-Power Optoelectronic Hybrid Devices
The rapid expansion of digitalization and the Internet of Things (IoT) is pushing existing information and communication systems to their limits in both data transmission and signal processing. Integrating electronics and photonics is therefore attracting attention as a key approach to overcoming these challenges. By combining optical devices with electronic components, it becomes possible to achieve faster data transfer and ultra-low power consumption. Beyond information and communication technologies, this optoelectronic fusion also holds promise for applications in quantum information, biosensing, and ultra-high-speed image sensors. Our research focuses on realizing true synergy between electronics and photonics through the development of optoelectronic hybrid devices based on Ge and GeSn, group IV semiconductor materials that are highly compatible with Si technology.
X-ray Topography for Advanced Wide-Bandgap Power Devices
Power devices are semiconductor components that convert and control electrical power and are widely used in automobiles, industrial equipment, and energy systems. As electricity demand continues to increase and environmental concerns become more pressing, the development of high-performance power devices that enable more efficient use of electric energy is becoming increasingly important. Although Si-based devices remain dominant, their performance is approaching its limits, and growing attention is being paid to wide-bandgap semiconductors such as SiC. However, unlike Si substrates, wide-bandgap semiconductor substrates often contain a high density of crystal defects, making defect engineering a critical issue. Our research aims to improve the reliability and productivity of next-generation power devices through crystal characterization and defect evaluation based on X-ray topography.
Ge-Based Materials for Thermoelectric Device Applications
Thermoelectric devices convert thermal energy directly into electrical energy through the Seebeck effect, in which a voltage is generated in response to a temperature difference across a material. Because semiconductors typically exhibit relatively large Seebeck coefficients, they can generate comparatively high voltages. In thermoelectric modules, p-type and n-type semiconductors, which produce voltages of opposite polarity, are paired and connected electrically in series. Silicon-germanium (SiGe) thermoelectric modules have already been used in high-temperature environments, including NASA space probes such as Voyager. In recent years, Sn-doped Ge-based materials have attracted growing interest for thermoelectric applications. Ge and Sn are both group IV elements and are highly compatible with Si technology, offering the potential for high-throughput manufacturing and lower cost. Compared with bismuth telluride, pure Ge has similar electrical conductivity and a slightly lower Seebeck coefficient, but its thermal conductivity is much higher, resulting in a low thermoelectric figure of merit (ZT). Alloying Ge with Sn is expected to improve performance in several ways: bandgap narrowing may enhance the Seebeck coefficient, improved carrier mobility can increase electrical conductivity, and enhanced phonon scattering caused by the heavy element Sn can reduce thermal conductivity. Owing to these combined effects, GeSn-based materials are promising candidates for achieving high ZT at room temperature. Our current research focuses on thermoelectric devices based on GeSn materials formed by laser-induced liquid-phase crystallization.
