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Prof. J. Lucy Shi
Compound semiconductor devices and materials for power conversion, photovoltaic, optoelectronic and other applications, as well as novel two dimensional materials such as graphene, transition metal dichalcogenides, etc.and devices based on the novel properties of these materials.
Recent awards/honors include:
Faculty Advising Award, University of Illinois at Chicago
Chinese Government Award for Outstanding PhD Student Abroad
De Kármán Fellowship established by Dr. Theodore von Kármán
Dr. Parijat Sengupta
Gallium Nitride is a wide and direct bandgap semiconductor. At its early stages, it was plagued by various unattractive characteristics such as difficult and expensive growth process, complicated fabrication processes and unexplained electrical phenomena. Through the past decade or two, many of these issues have been investigated and fabrication processes have matured. As a result of this progress, GaN has been incorporated into our everyday life; the fast data speeds (LTE) available in cell phones are made possible by GaN High Electron Mobility Transistors (HEMTs), blue LEDs (and as a result, white LEDs) are made from GaN technology, the high power electronics in electric vehicles are more efficient due to GaN transistors, even satellites and other space-voyage equipment have higher resiliency to radiation damage due to this robust material. However, the technology is still in its infancy and has so much more potential waiting to be unlocked.
My research involves fabricating devices such as Metal-Insulator-Semiconductor Heterojunction Field Effect Transistors (MISHFETs) to explore and optimize a few aspects of the fabrication process and improve the performance. Topics such as making better electrical (ohmic) contacts to the semiconductor, minimizing defects between the insulator and semiconductor interface, aiming for high breakdown voltage (several hundred volts), and millimeter-wave transistors are currently being investigated. Fabrication processing involves several standard semiconductor fabrication instruments such as physical and chemical vapor deposition, optical lithography, dry/wet etching and some involving state-of-the-art instrumentations such as electron-beam lithography or atomic layer deposition. Characterization tools such as Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Source-Measure Units (SMUs), for example, are also important tools describing the nature of a system. My interdisciplinary research is essential towards understanding and optimizing the transistors of the future.
Keywords: GaN, MISHFETS, fabrication, characterization
GaN power switching device has been broadly applied in the field of consumer electronics power supply, automotive (motor control), AC-DC (PFC) controller, photovoltaics inverter and hybrid/electric vehicle system (as a voltage booster and inverter between the battery and the motor). Besides power switching devices, GaN-based optoelectronics device has also attracted much attention. In addition, GaN are one of the most promising materials for ultraviolet (UV), near-infrared (IR) and Terahertz (THz) detectors due to its large LO phonon energy (92 meV) and ultrafast relaxed time (~140 fs).
One part of my PhD research focuses on TCAD modeling of GaN-based Power Switching Transistors. The aim is to explore and optimize structure to improve reliability of E-mode GaN MISHFETs, suppress RF current collapse and enhance breakdown voltage. The other part of research is on AlGaN/GaN quantum well Terahertz and Infrared Photodetectors. We are working on modeling of high-responsivity and high-detectivity novel quantum well photodetector, and seeking practical methods to eliminate dark current and enhance signal-to-noise ratio.
Keywords: GaN, AlGaN/GaN, MISHFETS, modeling, photodetector, quantum wells
Two-dimensional materials are supposed to be applied in the next generation nanodevices because of their easy fabrication and favorable physical properties. My research mainly focuses on the tunability of electronic, optical, mechanical properties in two-dimensional MoS2 with nanoengineering. Small molecules adsorption and dissociation on the monolayer MoS2 surface is also one focus of the research. The target is to better understand the relationship between nanoengineering and physical properties. For monolayer MoS2, the direct band gap character intrigues great interests for its application as transistors, light-emitting diodes and solar cells. But the low carrier mobility becomes a barrier for the MoS2-based field-effect transistors. Besides that, bandgap tuning is required in some electronic and photonics applications. It is one of aims that the nanoengineering will be able to tune the electronic properties of monolayer MoS2, which could be applied to adjust the performance of MoS2-based transistors, which could be applied to design chemical and biomedical sensors.
Keywords: Simulation, MoS2, nanoengineering
Albert Colon, PhD May 2017 now with Sandia National Laboratory
Chenjie Tang, PhD May 2017 now with Qualcomm
We are constantly looking for highly self-motivated postdocs and students on all levels (PhD, Master, Undergrad) who are interested in semiconductor devices and nanotechnology. Please contact Dr. Shi (email@example.com) for opportunities.