Research Overview:
In my research journey, I have consistently been engaged in the study on characterization of material physical properties and electronic device applications of "wide-bandgap (WBG) semiconductors." The term "wide-bandgap" refers to the property of having a large bandgap, indicating robust physical and chemical properties that make them unique in terms of resilience to high electric fields, ultra-high temperatures, and radioactive harsh environments. Particularly, their ability to withstand high electric fields is appealing for applications, allowing the fabrication of devices with high doping (high carrier density) and thin films for the same voltage rating. While silicon (Si) remains the protagonist king in current semiconductor technology, in power devices, such as those used in electric vehicles (Tesla and Toyota), railways (shinkansen and Yamanote Line, Hankyu), wide-bandgap semiconductors like silicon carbide (SiC) and gallium nitride (GaN) enable the production of devices with significantly higher breakdown voltages and lower losses than Si devices. SiC semiconductors are already being utilized in practical applications, contributing significantly to the efficiency and low power consumption of electrical systems. Furthermore, GaN transistors are also being implemented in rapid chargers for devices like PCs and tablets. This research field, attracting global attention, is considered a key player in achieving a sustainable and energy-efficient society. However, these materials have not fully unleashed their true potential, and continuous fundamental research is crucial for future performance improvements.
During my PhD at Kyoto University, under the guidance of Prof. Tsunenobu Kimoto, Prof. Jun Suda, and Prof. Masahiro Horita, I delved into the elucidation of the electronic properties of gallium nitride (GaN) semiconductors. Significant achievements include:
(1) Achieving nearly ideal avalanche breakdown for the first time in the world, through the design and demonstration of a novel beveled mesa structure that mitigates electric field concentration, demonstrating a record high parallel-plane breakdown field of 2.8-3.5 MV/cm. Maeda et al., IEDM 2018. Maeda et al., IEEE EDL 2019.
(2) Determining the impact ionization coefficient, which is one of the most important physical properties for power device applications, using a novel measurement technique based on unique high-field optical absorption (the Franz-Keldysh effect combined with p-/n+ junction). Maeda et al., IEDM 2019. Maeda et al., ISPSD 2019. Maeda et al., APL 2019. Maeda et al., JAP 2021.
(3) Clarifying the temperature and doping density dependence of the critical electric field of GaN from both material and device characteristic perspectives and successful modeling. Maeda et al., IEEE EDL 2022.
(4) Optical absorption indudced by high electric field (the Franz-Keldysh effect) and its photocurrent analysis in GaN, SiC and Ga2O3 devices. Maeda et al., APL 2018. Maeda et al., APEX 2018. Maeda et al., EMC 2023 (paper in preparation).
(5) Characterization of Schottky and p-n junctions, revealing important physical properties. Maeda et al., APEX 2017. Maeda et al., JJAP 2019.
Notably, these achievements, especially (1)-(3), garnered significant attention globally, being presented at prestigious international conferences such as IEDM and ISPSD in the fields of electronic devices and power devices. Awards such as the IEEE EDS Japan Joint Chapter Student Award (IEDM 2018, IEDM 2019) and ISPSD 2019 Charitat Award further highlighted the worldwide recognition.
At Cornell University (USA, NY), I worked on the electronic devices of the ultimate wide-bandgap semiconductor, aluminum nitride (AlN, bandgap 6.1 eV), and conducted research on the electronic properties and device applications of functional materials like scandium aluminum nitride (ScAlN), known for its high piezoelectricity, strong ferroelectricity, and high dielectric constant, under the supervisions of Prof. Huili Grace Xing and Prof. Debdeep Jena.
Leveraging these experiences, I am currently leading research group as a principal investigater (PI) at the University of Tokyo, establishing a laboratory focused on the fabrication and characterization of wide-bandgap semiconductors. Building upon the evaluation and device prototyping of materials like GaN and SiC, I aim to contribute, from a fundamental research perspective, to the realization of innovative and socially impactful electronic devices. Let's enjoy research!
