I am the very few students in china who won the first prize in the National High
School Physics Olympiad Competition, which guaranteed my admission to the
Department of Physics of Peking University, and still took and ranked 1% in the
unified college entrance examination. Studying among the best students of China after
entering college, I remained top 20% of the grade. However, grade point is not the
thing I only focus on. I always enjoyed the little ideas inspired by the courses.
The Bonn-Karman boundary condition was commonly used in the energy band theory
introduced in the course ‘Solid State Physics’ and it occurred to me that some
materials of new property might emerge when there were not so many primitive cells.
Then I browsed papers and found out nanoparticles and graphene ribbons were just
examples of this kind of confinement. When I learned about the idea of p-n junctions,
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I thought crazily that the ( C3 +3) kinds of contacts between metal, semiconductor and
insulator might all have their applications. Later on, I surprisedly found five of them
in a single device--field effect transistor.
In my sophomore year, I decided to start my scientific research. I chose to work in the
field of nano semiconductor. Aiming at replacing traditional silicon devices, the first
step is to fabricate high-performance transistors and logic gates. Thus I firstly focused
on the construction of low static power consuming inverters based on nanowire
MOSFETs. After growing high quality n-type CdS nanowires, I successfully repeated
the work of Schottky barrier modified n-channel CdS and p-channel Zn3P2 MOSFETs
with very low threshold voltages. Based on this, we fabricated complementary
inverters on an integrate p+-Si substrate via electric field assembly in which the p-type
nanowire was assembled on prepared ohmic contact electrodes, after which Schottky
contacts were made. The thus prepared inverters exhibit excellent performances and
the static power consumption was as low as 0.03nW, lowest for complementary
nanowire MOSFET inverters ever reported.
Later on, I joined another work of fabricating inverters, in which I mainly focused on
obtaining high voltage gain. In order to achieve this, thinner insulating layers were
needed to increase the gate capacitance; meanwhile, ensuring no leakage current.
Thus high dielectric constant HfO2 layers of 20nm were applied instead of SiO2. Two
top-gate MOSFETs based on n-type CdS nanobelts were first fabricated and the
inverter was constructed on them. Gains of 1000, 100 were each obtained with the
supply voltage of 10V, 1V respectively, highest of similar inverters so far. During my
research of nanowire devices, I found that although the devices were completely kept
from light by an aluminum box, the working stability is still obviously weakened
when put in a ‘noisy’ environment. This is an issue seriously restricting the
application of nanowire devices and I intend to do some research on this aspect later.
In order to get a bigger picture of semiconductor nanotechnology, I decided to do
research not only on electric devices, but also on optical devices. This time, I became
the research leader and picked the topic of fabricating organic-inorganic hybrid white
light-emission diodes. To make the emission peaks tunable, instead of using the
widely applied nanoparticles, size of which cannot be precisely controlled, I
synthesized ternary alloy nanobelts of CdSSe with continuously tunable component
and emission spectra. Considering the diffusion of indium into organic materials, I
chose p-type Si (p-Si) to be the anode instead of indium-tin-oxide to construct
top-emission devices. By doping nanobelts into a kind of blue emission polymer PFO
and by applying certain transporting layers and modulating the thickness of each layer
of the device, I successfully produced electroluminescence white light with the CIE
coordinate of (2.8, 3.1). A phenomenon of my device worth mentioning is that the
blue shift of emission of CdSSe nanobelts after doped into polymer PFO was as large
as 50 nm. Many works study on the blue shifts of nanoparticles but very few works
refer to nanobelts, in which the quantum confinement effect is not the main reason. So
the mechanism of energy-transfer of my device is the direction I’ll further my
research.
In my PhD program, I intend to proceed my study in the field of nanotechnology.
Performance enhancement of single FETs and logic gates is the first step to take to
fulfill the dream of replacing Si-based electronics. I find great joy in modulating
device structures, such as adding special contacts, applying newly high dielectric
media and even replacing metal electrodes with polymer ones. Meanwhile, exploring
novel materials always brings about a lot of excitement. Believing in that every
combination on the element table has its day, there’re still a lot to try on
homostructures. After combining elements, we combine materials and the world
becomes a lot more diversified when we do research on heterostructures. As one of
the most promising candidates of realizing our nano-people’s dreams, carbon
nanotubes and graphene have always attracted me. Their small diameters, special
energy band structures, magic transport properties, amazing orderliness after
self-assembly and the voltage controllable p/n type conversion make me longing for
doing research on them fervently. Another mountain we need to climb to reach our
dreams is the patterning of nanostructures and the integration of electronic
components. This is a tough task but it’ll be my honor if I get a chance to do research
on such a challenging topic. Compared to the heaviness of replacing Si-based
electronics, I always feel brightly that a major breakthrough is about to take place in
the solid state lightening and solar cells in the near future. Devices like LEDs and
ambipolar FETs intrigue my interest greatly and I hope to study both on the
underlying mechanism and the performance enhancement of the devices.
I choose to apply to the Department of Electrical and Computer Engineering, Ohio
State University for PhD program not only because OSU has the world’s top class
program for Electrical Engineering, but also there are a number of devoted groups,
such as the group of Prof. Ringel, Prof. Wu Lu and Prof. Brillson, whose projects
highly related to my research experience and highly coincide with my interest. I
believe in your department, I can get the best ever education. On the other hand, as a
student who simultaneously has excellent academic records, extremely high standard
test scores and particularly abundant research experience, I am fully confident that I
can make a contribution to your department in the following years of PhD study.