10/24/2018 Janet McGreevy, MNTL 6 min read
Written by Janet McGreevy, MNTL
In September, ECE ILLINOIS graduate student Patrick Su and fellow co-authors Professor John Dallesasse and PhD student John Anthony Carlson, II, were awarded the "Student Presentation Award" at TECHCON for a presentation on "GaN-based mach-Zehnder Modulators for Highly Efficient Optical Modulation and Switching Applications".
SRC TECHCON is a conference hosted by the Semiconductor Research Corporation (SRC), that invites students funded under their programs to present and interact with SRC company representatives. SRC is a research consortium connected with semiconductor companies including Intel, Microsoft, Analog Devices, and IBM, that help fund research in order to push the next-generation of semiconductor research. Such research is closely related to the needs or interests expressed by its member companies. At SRC TECHCON, companies are able to send representatives to interact with the students working on the projects to provide feedback, encourage discussions, and ultimately to also recruit top talent for their companies once the students graduate.
Su, who is currently in his last semester of an MS degree in electrical and computer engineering, will receive his degree this December. Su initially chose Illinois for his bachelor’s degree in electrical engineering because it is a highly ranked school, while still close to his home in Geneva, Illinois. He intends to continue his academic journey by pursuing a PhD degree, with his advisor, Professor John Dallesasse. Regarding this decision, he said "Professor Dallesasse's mentorship was why I chose to stay at Illinois above any other graduate schools. His research interests are so closely aligned to what industry, what companies are looking into, it’s what made it so compelling to join his group as a PhD student."
When asked about the impact of the presentation’s topic, Su responded "For high-performance computing, such as in data centers, supercomputing, and next-generation applications that demand higher processing powers with lower energies, many people are starting to migrate towards employing photonic systems to overcome the limitations of traditional electrical interconnects, such as copper wires. However, electrical signals--your zeroes and ones from a computer--still need to be imprinted onto your optical signal via modulation. The issue with current modulators is that they are hard to integrate with CMOS processes or they are naturally inefficient modulation material. GaN is an interesting material that has gained a lot of traction recently. Its large bandgap, the ability to facilitate a two-dimensional electron gas layer, 2DEG, in between AlGaN/GaN, has drawn a lot of people to base 5G electronics and high-power amplifiers on GaN. While there has been a large amount of interest using GaN for electronic devices, there has not been a large amount of data showing the exploration of GaN for photonic device applications. This is what led us to use GaN for optical modulators. GaN has a non-centrosymmetric crystal structure, strong polorization, and strong built-in fields with an ability to support a 2DEG layer that make it a compelling candidate for highly efficient optical modulation and switching structures. The ability of GaN to be grown on silicon also presents the opportunity to integrate with CMOS technology on a native substrate that can lower the manufacturing costs as well as provide a platform to easily integrate other supporting modules onto the GaN optical modulating/switching structure."
It was during his freshmen year summer, when he had a month between the end of the spring semester and the start of his study abroad research program in Taiwan through International Programs in Engineering (IPENG), that he decided to take advantage of his remaining time on campus. While looking for professors to conduct research with, to fill the gap over the summer and possibly continue conducting research when he came back from Taiwan, he discovered Professor John Dallesasse's group. Dallesasse’s group focuses on next-generation III-V semiconductor devices for photonic integrated circuits, optical device integration with CMOS circuitry, and also three-terminal-based long-wavelength emitters.
Su reflected on this time in his academic career: "Finishing only my freshmen year of undergrad, I barely knew anything about quantum mechanics, or device physics, let alone semiconductors. Regardless, after many talks of my interest in getting involved with his group, Professor Dallesasse allowed me to help characterize some vertical-cavity surface-emitting lasers (VCSELs) that his graduate students were working on. One of Professor Dallesasse's graduate students began to show me how to characterize VCSELs for their light-current-voltage (L-I-V) characteristics, a standard way of benchmarking the performance of a semiconductor laser. As he began to slowly turn the dial on the current meter that increased the injection of electrons into the device, you could begin to see a soft glow of light that was emerging from the top of the device, spontaneous emission, by looking into a CMOS camera. CMOS image detectors let you visualize light in the near-infrared that our eyes typically cannot see. As he began to slowly apply increased current, we reached threshold and suddenly, the soft glow of light that was emitting in all directions focused in a single column of light. It was probably one of the most fascinating experiences I have ever had in my life. It was really in that moment that I knew I wanted to pursue research in optoelectronic devices."
After earning his PhD degree, he wants to pursue a career in an R&D division in industry. He explained "I think at this moment, there's momentum gaining in the laser industry. With newer emerging applications such as 3D sensing for facial recognition software, LIDAR for autonomous driving and even VR applications, I think there could be some very exciting opportunities in the next several of years. Being at SRC TECHCON and receiving the presentation award, as well as so much positive feedback from the company liaisons, it was very motivating and encouraging that I was going in somewhat the right direction. I think it’s very exciting to be in this field right now and I'm anxious to see where I'll end up after graduating. I feel extremely grateful for Professor Dallesasse's guidance and the breadth of knowledge that being in his group has been able to give me. Finding his group my freshmen year of undergrad will probably end up being one of my most fortunate moments in my life and I feel grateful for this university for all that it's been able to help me achieve so far."
His current research efforts are focused on the many different projects that Professor Dallesasse believes may have strong potential relative to current industry needs, including: GaN-based Mach-Zehnder Modulators; the Transistor-Injected Quantum Cascade Laser (TI-QCL); High-Power Single-Mode Vertical-Cavity Surface-Emitting Lasers (VCSELs); and, the 4CeeD project.
Su noted that "MNTL has been close to a second home for me. There have been a great many people in MNTL, from professors, fellow graduate students, and MNTL cleanroom staff, that have been able to give me a wide perspective of different views on research problems."