Raphael Tsu (born December 27, 1931)
is a Fellow of the
American Physical Society and is
Professor Emeritus
''Emeritus'' (; female: ''emerita'') is an adjective used to designate a retired chair, professor, pastor, bishop, pope, director, president, prime minister, rabbi, emperor, or other person who has been "permitted to retain as an honorary title ...
of
electrical engineering at the
University of North Carolina at Charlotte
The University of North Carolina at Charlotte (UNC Charlotte or simply Charlotte) is a public research university in Charlotte, North Carolina. UNC Charlotte offers 24 doctoral, 66 master's, and 79 bachelor's degree programs through nine colle ...
, Charlotte, NC.
Early life and education
Tsu was born to a Catholic family in Shanghai, China, in 1931. As a child he was inspired by his great uncle who in 1926 was amongst the first six Chinese bishops ever to be consecrated at the Vatican in Rome and as a teenager by his US-educated father, Adrian, and French-educated uncle, Louis. His paternal grandfather and great uncle were pioneers in power plant and modern shipyard in Shanghai. While leaving Shanghai, his great uncle, on his death bed told him to remember the old Chinese saying that to succeed requires the right tool.
Tsu initially emigrated to the west in 1952 to study physics at Medway Technical College in England for one year before leaving for Dayton, OH, the following year. He earned the bachelors of science at the
University of Dayton
The University of Dayton (UD) is a private, Catholic research university in Dayton, Ohio. Founded in 1850 by the Society of Mary, it is one of three Marianist universities in the nation and the second-largest private university in Ohio. The univ ...
in 1956 and spent one semester at Carnegie Institute of Technology (predecessor to
Carnegie Mellon University) before going to
Ohio State University
The Ohio State University, commonly called Ohio State or OSU, is a public land-grant research university in Columbus, Ohio. A member of the University System of Ohio, it has been ranked by major institutional rankings among the best publ ...
to earn an M.S. in 1957 and a Ph.D. in 1960. At Ohio State, Tsu worked primarily under Robert Kouyoumjian.
Career
After several years working as a member of the technical staff at
Bell Laboratories
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),
then AT&T Bell Laboratories (1984–1996)
and Bell Labs Innovations (1996–2007),
is an American industrial research and scientific development company owned by mult ...
(BTL) at Murray Hill, NJ, developing an ultrasonic amplifier, a mechanism invented by D. L. White, Tsu moved to the IBM,
T.J. Watson Research Center in
Yorktown Heights, NY
Yorktown Heights is a census-designated place (CDP) in the town of Yorktown in Westchester County, New York, United States. The population was 1,781 at the 2010 census.
History
Yorktown Heights is in the town of Yorktown, New York, in norther ...
as an associate to
Leo Esaki
Reona Esaki (江崎 玲於奈 ''Esaki Reona'', born March 12, 1925), also known as Leo Esaki, is a Japanese physicist who shared the Nobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his work in electron tunneling i ...
beginning a well-known collaboration that yielded a theory of man-made quantum materials,
superlattice
A superlattice is a periodic structure of layers of two (or more) materials. Typically, the thickness of one layer is several nanometers. It can also refer to a lower-dimensional structure such as an array of quantum dots or quantum wells.
Disc ...
s and
quantum wells.
Tsu later joined the Amorphous Semiconductors Institute (ASI) and directed energy research at Energy Conversion Devices (ECD) near Detroit, MI, as invited by inventor
Stan Ovshinsky. His contribution included the first experimental determination of the
volume fraction
In chemistry and fluid mechanics, the volume fraction φ''i'' is defined as the volume of a constituent ''V'i'' divided by the volume of all constituents of the mixture ''V'' prior to mixing:
:\phi_i = \frac
Being dimensionless, its unit is ...
of crystallinity for conductivity percolation in
amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
and
ermanium and providing experimental proof of the existence of an intermediate order. He discovered experimentally that post annealing with H
2 and O
2 can drastically remove
dangling bond
In chemistry, a dangling bond is an unsatisfied valence on an immobilized atom. An atom with a dangling bond is also referred to as an immobilized free radical or an immobilized radical, a reference to its structural and chemical similarity to a f ...
defects in
amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
.
From 1985 to 1987, Tsu served as the amorphous silicon program group leader at the
National Renewable Energy Laboratory
The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research an ...
(then known as SERI, Solar Energy Research Institute) in
Golden, CO
Golden is a home rule city that is the county seat of Jefferson County, Colorado, United States. The city population was 20,399 at the 2020 United States Census. Golden lies along Clear Creek at the base of the Front Range of the Rocky Mountai ...
. His theoretical derivation of the relationship between
optical absorption
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). ...
and disorder in amorphous silicon and germanium in terms of fundamental constants shows that the slope of the
Tauc plot
A Tauc plot is used to determine the optical bandgap, or Tauc bandgap, of either disordered or amorphous semiconductors.
In his original work Jan Tauc () showed that the optical absorption spectrum of amorphous germanium resembles the spectrum o ...
is uniquely determined by the oscillator strength of the transition, the deformation potential, and the mean deviation of the atomic coordinates obtained from the RDF.
In 1972, Tsu organized a group and was invited by the
Chinese Science Academy that resulted in the first report on the technology in
China published in
Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...
. This led to his involvement through establishing the first Chinese Scientific delegation visit to the US invited by the US-China Relations Committee of the US Academy of Science. During this visit, he worked with the
US State Department
The United States Department of State (DOS), or State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs of other nati ...
for the program and logistics on the East Coast. This effort contributed to the opening of scientific exchange between the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
and China.
Invention of the superlattice
Of all his contributions, Tsu's most important impact has been in the invention of spatially modulated, or periodically layered, materials – the
superlattice
A superlattice is a periodic structure of layers of two (or more) materials. Typically, the thickness of one layer is several nanometers. It can also refer to a lower-dimensional structure such as an array of quantum dots or quantum wells.
Disc ...
. The structure of a superlattice has remained a highly productive innovation in nanoelectronics well into this century. Indeed, Tsu played a pivotal role in the creation, invention, and development of synthetic periodic superlattice materials and devices that functionally depend on these artificially fabricated two-dimensional multiple-quantum well structures while working in
Leo Esaki
Reona Esaki (江崎 玲於奈 ''Esaki Reona'', born March 12, 1925), also known as Leo Esaki, is a Japanese physicist who shared the Nobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his work in electron tunneling i ...
’s Exploratory Device Research Group in the IBM Watson Laboratories. Tsu introduced the idea of alternating layers of different material, A/B, with the correct band-edge offset. While at IBM, Tsu worked closely with another notable scientist, the late L. L. Chang. Ray's theoretical analysis at IBM led to the important concept of modulation doping for carrier mobility enhancement independently of, and prior to, the work of Dingle, et al. at Bell Labs.
Contributions to other technologies
These pioneering contributions have led to many current technologies including terahertz oscillators, negative differential conductance (NDC) in the I-V characteristics of superlattice devices, resonant tunneling quantum well (double barrier) structures, of phonon band folding and the related Raman spectra, and the discovery of forbidden phonon modes. Raphael Tsu's other contributions have impacted a wide range of materials science.
A
leitmotif in Tsu's career has been ubiquitous electron–lattice interactions in materials as well as quantum transport. One of his first publications from Bell Labs is concerned with radiation of phonons by non-accelerating charges. Another from IBM,
is related to phonons and polaritons. He and
Timir Datta
Timir Datta is an Indian-American physicist specializing in high transition temperature superconductors and a professor of physics in the department of Physics and Astronomy at the University of South Carolina, in Columbia, South Carolina.
Earl ...
have introduced the concept of wave impedance in quantum transport for dissipation-free quantum waves,
where using the expressions for probability continuity and energy expectation an equation for quantum wave impedance of Schrödinger functions is obtained.
Notable Papers
The following two papers were amongst the 50 most cited articles to appear in the first fifty years of the journal
Applied Physics Letters
''Applied Physics Letters'' is a weekly peer-reviewed scientific journal that is published by the American Institute of Physics. Its focus is rapid publication and dissemination of new experimental and theoretical papers regarding applications ...
published by the
American Institute of Physics
The American Institute of Physics (AIP) promotes science and the profession of physics, publishes physics journals, and produces publications for scientific and engineering societies. The AIP is made up of various member societies. Its corpora ...
(AIP) and were featured as such in APL's 50th anniversary issue http://apl.aip.org/apl_50th_anniversary .
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References
External links
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{{DEFAULTSORT:Tsu, Raphael
1931 births
Fellows of the American Physical Society
Living people
Ohio State University College of Engineering alumni
Scientists from Shanghai
Semiconductor physicists
University of Dayton alumni
University of North Carolina at Charlotte faculty