My goal is to become a proficient researcher on advanced materials such as 2D
materials and III-V materials due to the following reasons. Firstly, in the era of postMoore’s
law, these materials have become increasingly important for their application
in either the trend of “More than Moore” or “Beyond CMOS”. Secondly, I plan to
dedicate myself to the development of semiconductor devices owing to my enthusiasm
at research. Therefore, to fulfill my goal, I am writing for applying the Ph.D. program
in EE at Yale University, which will be the best choice for me due to your eminent
academic achievement and highly esteemed reputation.
The undergraduate study in Material Science and Engineering (MSE) provided me
with not only views of material properties such as lattice structures and grain boundaries,
but also methods of material characterization like AFM, Raman spectroscopy, SEM and
TEM. Among all curriculum, I was most interested in the courses relevant to solid-state
electronics. After taking the courses instructed by Prof. Miin-Jang Chen, I was
fascinated by semiconductor devices and their industrial application. Hence, I took the
special project course by Prof. Chen and learned the process of atomic layer deposition
(ALD). To further extend my knowledge, I applied for Graduate Institute of Photonics
and Optoelectronics at National Taiwan University (NTU) and joined Prof. Chao-Hsin
Wu’s research group.
In Prof. Wu’s group, I equipped myself with abilities to measure the electrical
characteristics, analyze the results and fabricate semiconductor devices. In Si FinFETs
project, I learned the principles of electrical measurement and measured I-V
characteristics of Si FinFETs at room and cryogenic temperatures. Totally 240 devices
with multiple geometry were measured, where on current, mobility, subthreshold swing
and drain induced barrier lowering (DIBL) were systematically analyzed. On the other
hand, I became skillful with device fabrication process and familiar with the working
principles of GaN High Electron Mobility Transistors (HEMTs). I was able to complete
the devices by photolithography, metal deposition and rapid thermal annealing. In
addition, I studied the principle of Ohmic contacts formation for GaN HEMTs and
theories of transfer length method (TLM), and extracted the contact resistance from
practical devices.
Furthermore, I exhibited my capability to research comprehensively in the 2D
materials project collaborated with Taiwan Semiconductor Manufacturing Company
(TSMC) and achieved great academic results. In developing BP transistors, I produced
and transferred few-layered BP by mechanical exfoliation, and then used electron-beam
lithography to define the patterns followed by metal deposition and lift-off process. After several refinement of the experiments, I successfully demonstrated a black
phosphorus transistor with a high hole mobility of 340 cm2
/Vs. In improving metal
contacts of BP transistors, I devoted myself to developing a novel doping method
enabling metallic Ohmic contacts to be formed at source/drain (S/D) region. After a
total number of thirty meetings with Dr. Yu-Ming Lin, a deputy director in TSMC, a
record low contact resistance of 0.365 k???m was achieved and metallic properties
were demonstrated. Moreover, the results were published in Scientific Reports and
successfully applied for a patent. In developing 2D heterostructures, I built up a 2D
heterostructure stacking process by myself. Taking advantage of this technique, I
stacked graphene/MoS2 heterostructures, where graphene served as the leading contacts
to MoS2 channel, thus achieving a high mobility of 116 cm2
/Vs by improving S/D
contacts. The results were published in AIP Advances. In addition, the heterostructures
of graphene-contact MoS2 fully encapsulated by top and bottom h-BN demonstrated
the improvement of mobility and hysteresis.
In the project of 2D materials, I also enhanced my ability to solve problems
encountered in the research. For instance, when investigating metal/BP contacts, I
discovered the deviation in extracting Schottky barrier height (SBH) and proposed a
modified method with a more reasonable value. The results were submitted to Journal
of Physics D: Applied Physics. To develop 2D heterostructures, I also set up a
homemade station, where 2D materials can be finely stacked within a short time.
Furthermore, to improve contact resistance of BP transistors, I figured out a process not
only achieving metallic doping at S/D region but also improving overall electrical
performance including ION/IOFF ratio, on current and mobility.
Most importantly, I found my enthusiasm at research on advanced materials in my
graduate study. After accomplishing some great works on 2D materials, I craved for
more insights and breakthroughs to make more contributions to semiconductor industry.
Advanced materials such as III-V materials, 2D materials and germanium are promising
due to their highly regarded potential for future application, and can thus gratify my
attempts.
In sum, I hope to continue the research at your graduate school because
Department of EE at Yale University is consistently a worldwide top-ranked EE school
with not only complete and advanced facilities, but also tremendous academic
achievements, and best of all, the extraordinary faculties. I am particularly interested in
the academic works by Prof. Fengnian Xia, who has achieved outstanding results in
electronics of 2D materials. The work on synthesis of thin-film BP by Prof. Xia is also
impressing, which plays an important role in industrial application of BP. Most
importantly, I believe I am an ideal candidate for your school. After the training at NTU,
I am confident that I am well qualified and can independently execute a research project with my ability to fix problems. With proficient skills and professional attitudes, I also
believe I can quickly involve myself into the research and make contributions
immediately. Furthermore, my motivation to investigate into the semiconductor fields
is intense. I will be very honored to study at one of the best EE schools, which will
enable me to reach my goal.