Jung-Hun Seo - US grants

The wide bandgap semiconductors have the potential for having better power conversion efficiency and higher current handling capability. Among various wide bandgap semiconductors, b-Ga2O3 has a stable thermodynamic property with a large bandgap and high electron mobility which makes it an attractive semiconductor candidate for next-generation power electronics and optoelectronics. Despite promising material property of b-Ga2O3, two well-known deficiencies of b-Ga2O3, namely, the poor thermal conductivity and the lack of efficient p-type dopant largely prohibit the use of b-Ga2O3 toward wider spectrum power electronics. This proposal aims to address the unipolar doping challenge and poor thermal property of n-type b-Ga2O3 by heterogeneously integrating with p-type single crystalline diamond, which allows us to bond two dissimilar semiconductors without restricted by lattice constants of b-Ga2O3 and diamond. To create a novel n-type b-Ga2O3 and p-type diamond heterojunction, an ultra-thin form of semiconductor, also called semiconductor nanomembranes, will be used. Building upon this, the specific objective of the proposed project is to realize the new class of ultra-wide bandgap high power heterojunction bipolar transistors based on the multiple p-n junctions using p-type diamond nanomembrane and n-type b-Ga2O3 nanomembrane. The outcome of the proposed research will result in the development of high power electronic devices operating at higher power density level, which could revolutionize power distribution and conditioning, allow for a more versatile and stable power system with the improved power conversion or handling efficiencies toward future high-power electronics.


The proposed research aims to develop the new class of ultra-wide bandgap high power device based on the novel heterogeneous integration method. It will provide a comprehensive solution to develop a completely new class of highly efficient high-power switches which will lead to greatly enhanced switching performance metrics over that of today's power electronics. We expect that upon the success of this project, the related commercialization will experience a significant change toward employing our new heterojunction technology in many possible ways. This research will also help train the next generation of scientists/engineers who will work at the interface of physics, materials science, and engineering. During the project period, various educational and outreach activities will be given at several different levels, including graduate, undergraduate, K-12, and community. The vision of this program is to provide these students with hands-on, interdisciplinary experiences in computational simulation and experimental research topics for tackling current technological and societal challenges. The project will provide excellent opportunities to educate and train undergraduate and graduate students, who will be exposed to various interdisciplinary fields of materials science and semiconductor nanoscience.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This major research instrumentation project is to acquire a high-performance Electron Beam Lithography system for research, education and broader impact in the Western New York region. The system uses an ultra-narrow beam of high energy electrons (1.8 nm wide) to define features on the scale of tens of nanometers. The unique capabilities of this advanced nanofabrication tool will enable crucial research in a broad range of fields spanning engineering, physics, chemistry, materials science and biology. The state-of-the-art tool will be installed at the University at Buffalo and provide both onsite and remote access to a large number of students, faculty, researchers and entrepreneurs across the region. The unique feature of the tool is the ability to define sub-10 nm dimension structures with fast writing speed over large areas. This feature is very important for cutting edge research in electronics and photonics. The aim is to rapidly translate the fundamental knowledge gained in academic laboratories to real world applications. Another feature of the tool is the ability to define nm structures on flexible substrates that are essential for biomedical applications. Undergraduate and graduate students in the engineering and science disciplines will have access to the tool. They will be trained in its use through courses and programs offered by the electrical engineering department at the University at Buffalo. The tool will enable cutting-edge research across computing, communications, healthcare, and education. The research opportunity given to undergraduate and graduate students will help build the skills of the future workforce for knowledge-based economy and maintain the economic competitiveness of the US. The tool will improve the research infrastructure in the western New York region and positively impact the economy of the region. The remote access feature will enable students to submit their designs for fabrication from any location. The instrument will also contribute to strong outreach programs in engineering and applied sciences. Investigators will provide mentorship to underrepresented students in science and engineering.

Electron beam lithography is an indispensable tool for advanced research in electronics, photonics, physics, and materials science. The tool will enable research in a broad range of topics: low power non-volatile high speed ferroelectric and magneto-electric based logic and memory devices for energy efficient data intensive computing applications; emerging low power and efficient quantum devices; nano-electronics based on two-dimensional (2D) materials; high power flexible electronics based on widebandgap semiconductors; room temperature THz devices based on coupling of optical phonons in III-V semiconductors to graphene plasmonic structures; understanding of the fundamental physics in correlated electron systems; THz plasmonic structures for chemical and biological sensing; graphene plasmonic array for THz communication; and characterization of 2D materials, heterointerfaces, and devices. These high impact research have applications that range from computing, communication, energy and health. It will also help in understanding fundamental physics in correlated materials and the switching dynamics in technologically important antiferromagnetic oxides. The proposed tool to be acquired will have large acceleration voltage, sub-10nm lithographic resolution, high beam position resolution, sub-20 nm stitching and overlay accuracy, tunable field size up to 3000 micrometers for high throughput writing, and height correction feature for writing on flexible substrates. These unique features are essential to carry out the proposed research.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This project aims to both understand the science and develop engineering of an emerging ultra-widebandgap semiconductor, gallium oxide, for the next generation high voltage, high current power electronics. Power electronics plays an essential role in several innovative technologies including integration of renewables to grid, electric cars, planes, and ships to name a few. The multidisciplinary team addresses several challenges spanning from the synthesis of low defect density materials to applications and benchmarking of device prototypes in high power converters. An important challenge in high power applications is the ability to manage heat dissipation during the device operation. This project addresses this challenge by integrating gallium oxide with a high thermal conductivity material which can efficiently dissipate heat. Additionally, innovative device designs and circuit topologies will be developed for high voltage, high power and low loss operation. Success in the program would enable power device and circuit technologies beyond the state-of-the-art technologies. The new technology would foster innovation in power electronics market. The fundamental study aspects of the project would increase the understanding of the electronic properties of ultra-widebandgap semiconductors which have applications beyond power electronics. The education and training of the diverse students working on the project would enhance their technical skills in semiconductor manufacturing. Domestic semiconductor manufacturing is currently a national priority for US economic leadership and national security. Educational outreach activities will be integrated with research tasks. The goal of the outreach efforts is to inculcate interest of middle and high school students to science and engineering fields, specifically targeting students from underrepresented minorities (URM). <br/><br/>Beta-gallium oxide (Ga2O3) has achieved robust maturity with low background doping densities, excellent doping control and electron mobilities reaching theoretically predicted values. The large predicted and experimentally demonstrated electric field strengths and good electron mobility makes it an attractive semiconductor for high voltage (> 10 kV) rating power devices. Such high voltage ratings can be achieved in thin drift layers that can be grown with low defect densities and high uniformity by metal organic chemical vapor deposition (MOCVD). The project leverages the experimental demonstration of in-situ Mg doped current blocking layers grown by MOCVD. The team has also demonstrated integration of gallium oxide onto high thermal conductivity substrates. The scientific objectives of this project are (i) developing and optimizing in-situ Mg doped current blocking and thick Ga2O3 drift layers with low controllable doping for high voltage and high power operation; (ii) design, fabrication, and measurement of high power MOSFETs with high breakdown blocking capability; (iii) heterogeneous integration of the power devices onto high thermal conductivity substrates for thermal management and (iv) investigation of switching losses and paralleling techniques, as well as benchmarking of practical circuits using the developed power devices. If successful, the proposed innovative device will enable efficient high-power switches with beyond 10 kV voltage ratings thus drastically reducing the cost and increasing the efficiency of high-power circuits. These technologies can accelerate the integration of renewables to the grid and lead to truly smart grid operation. The integrated education plan aims to educate and motivate young students, especially female students, and those from the URM groups, to pursue STEM studies and careers by direct participation in the proposed research activities. The research opportunity given to undergraduate and graduate students will help build the skills of the future semiconductor workforce for domestic manufacturing and maintain the economic competitiveness of the US.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.