Research Projects

LeeLab's research is at the intersection of Materials Science, Applied Physics, and Electrical Engineering, with a particular interest in ultra-wide bandgap oxide semiconductors, solid-state electronics, and microscopy characterization. Our goal is to enable next-generation high-performance power electronics by addressing device-level critical challenges with scientific/engineering approaches. In addition to Prof. Lee's individual lab space in the RFM Building, the group's research activities are conducted in the core research facilities at Texas State University, including the Nanofabrication Research Service Center (NRSC) and the Analysis Research Service Center (ARSC).

Ultra-Wide Bandgap Oxide Materials & Devices

Wide- & ultra-wide-bandgap (WBG & UWBG) compound semiconductors (eg. SiC, GaN, Ga2O3, and AlN) hold tremendous potential for next-generation power electronics and RF applications due to their ability to enable devices with high critical E-fields and low switching losses. Among these, oxide ultra-wide-bandgap semiconductors, known for their excellent air and thermal stability, have generated considerable interest in their device applications. However, to excel in the power electronics market, unipolar materials systems like Ga2O3 require a flexible fabrication process, innovative device architecture, and a comprehensive understanding of metal-semiconductor junctions to demonstrate superior device characteristics. In this project, our group develops device-enabling key process/integration knowledge and examines the electrical properties of UWBG oxide semiconductors. In addition, guided by theoretical insights, emerging semiconductor systems and their applications will be explored.

Gate Stack and Interface Engineering

Transistors with excellent gate control are at the heart of contemporary and emerging devices. In advanced technology, unique challenges have arisen owing to the integration of 3-D architecture. This requires innovative solutions for the gate stack that do not compromise performance. For power devices utilizing WBG or UWBG semiconductor operating at high electric fields and high temperatures, surface and interfacial reactions can significantly degrade device characteristics and reliability. To address these issues, an alternative approach is necessary to engineer the material interfaces. In this part of the research, our group uses diverse synthesis, growth, and deposition methods to create tailored gate stacks and metallization for electronic/optoelectronic devices intended for harsh environment conditions, such as high-temperature, intense-radiation, and deep-space applications.

Advanced Microscopy Characterization for Semiconductors

Apart from the great potential of WBG materials, one of the primary challenges is their tendency to form defects readily, which can dictate device performance. From theoretical calculations, numerous crystalline imperfections are very common in the bulk of the substrates. However, experimental evidence on this subject is limited to indirect surface characterization techniques rather than direct bulk characterization from cross-sectional S/TEM. In addition, the presence of atomic defects requires careful, accurate, and efficient analysis methodology. In this research direction, our group aims to bridge the gap between the performance of WBG semiconductors and theoretical calculations by utilizing advanced microscopy and metrology techniques. In addition, other semiconductors and electronic materials systems, where identifying defects is of interest, can benefit from the microscopy methodology developed here and can accelerate the learning and improvement.