Raphael Tsu

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Raphael Tsu
Raphael "Ray" Tsu.jpg
Born (1931-12-27) December 27, 1931 (age 92)
NationalityAmerican
Other namesRay Tsu
Alma mater
Known for resonant tunneling diode, Tsu–Esaki formula
Awards Alexander von Humboldt Award (1975)
James C. McGroddy Prize for New Materials (1985)
Scientific career
Fields Electrical engineering
Institutions
Thesis The theory and application of the scattering matrix for electromagnetic waves  (1960)
Doctoral advisor Thomas Tice
Robert Kouyoumjian
Website ece.charlotte.edu/directory/dr-raphael-tsu-phd

Raphael Tsu (born December 27, 1931) [1] is a Fellow of the American Physical Society and is Professor Emeritus of electrical engineering at the University of North Carolina at Charlotte, Charlotte, NC. [2]

Contents

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.[ citation needed ]

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 in 1956 and spent one semester at Carnegie Institute of Technology (predecessor to Carnegie Mellon University) before going to Ohio State University to earn an M.S. in 1957 and a Ph.D. in 1960. At Ohio State, Tsu worked primarily under Robert Kouyoumjian. [1]

Career

After several years working as a member of the technical staff at Bell Laboratories (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 as an associate to Leo Esaki beginning a well-known collaboration that yielded a theory of man-made quantum materials, superlattices 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 of crystallinity for conductivity percolation in amorphous silicon and [germanium], [3] and providing experimental proof of the existence of an intermediate order. [4] He discovered experimentally that post annealing with H2 and O2 can drastically remove dangling bond defects in amorphous silicon.

From 1985 to 1987, Tsu served as the amorphous silicon program group leader at the National Renewable Energy Laboratory (then known as SERI, Solar Energy Research Institute) in Golden, CO. His theoretical derivation of the relationship between optical absorption and disorder in amorphous silicon and germanium in terms of fundamental constants shows that the slope of the Tauc plot is uniquely determined by the oscillator strength of the transition, the deformation potential, and the mean deviation of the atomic coordinates obtained from the radial distribution function (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. [5] 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 for the program and logistics on the East Coast. This effort contributed to the opening of scientific exchange between the United States 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. The structure of a superlattice has remained a highly productive innovation in nanoelectronics well into the 21st 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’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 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. [6]

Contributions to other technologies

These pioneering contributions have led to many current technologies including terahertz oscillators,[ citation needed ] negative differential conductance (NDC) in the I-V characteristics of superlattice devices, [7] resonant tunneling quantum well (double barrier) structures, [8] of phonon band folding and the related Raman spectra, and the discovery of forbidden phonon modes. [9] 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 [10] is concerned with radiation of phonons by non-accelerating charges. Another from IBM, [11] is related to phonons and polaritons. He and Timir Datta have introduced the concept of wave impedance in quantum transport for dissipation-free quantum waves, [12] where using the expressions for probability continuity and energy expectation an equation for quantum wave impedance of Schrödinger functions is obtained.

Selected publications

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 published by the American Institute of Physics (AIP) and were featured as such in APL's 50th anniversary issue http://apl.aip.org/apl_50th_anniversary .

Related Research Articles

In condensed matter physics and materials science, an amorphous solid is a solid that lacks the long-range order that is characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymously with amorphous solid; however, these terms refer specifically to amorphous materials that undergo a glass transition. Examples of amorphous solids include glasses, metallic glasses, and certain types of plastics and polymers.

<span class="mw-page-title-main">Leo Esaki</span> Japanese physicist (born 1925)

Reona Esaki, 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 in semiconductor materials which finally led to his invention of the Esaki diode, which exploited that phenomenon. This research was done when he was with Tokyo Tsushin Kogyo. He has also contributed in being a pioneer of the semiconductor superlattices.

<span class="mw-page-title-main">Polariton</span> Quasiparticles arising from EM wave coupling

In physics, polaritons are bosonic quasiparticles resulting from strong coupling of electromagnetic waves (photon) with an electric or magnetic dipole-carrying excitation (state) of solid or liquid matter. Polaritons describe the crossing of the dispersion of light with any interacting resonance.

Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the scanning tunneling microscope, an instrument for imaging surfaces at the atomic level. The first successful scanning tunneling microscope experiment was done by Gerd Binnig and Heinrich Rohrer. The key to their success was using a feedback loop to regulate gap distance between the sample and the probe.

A superlattice is a periodic structure of layers of two 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.

Quantum-cascade lasers (QCLs) are semiconductor lasers that emit in the mid- to far-infrared portion of the electromagnetic spectrum and were first demonstrated by Jérôme Faist, Federico Capasso, Deborah Sivco, Carlo Sirtori, Albert Hutchinson, and Alfred Cho at Bell Laboratories in 1994.

Car–Parrinello molecular dynamics or CPMD refers to either a method used in molecular dynamics or the computational chemistry software package used to implement this method.

A resonant-tunneling diode (RTD) is a diode with a resonant-tunneling structure in which electrons can tunnel through some resonant states at certain energy levels. The current–voltage characteristic often exhibits negative differential resistance regions.

A charge density wave (CDW) is an ordered quantum fluid of electrons in a linear chain compound or layered crystal. The electrons within a CDW form a standing wave pattern and sometimes collectively carry an electric current. The electrons in such a CDW, like those in a superconductor, can flow through a linear chain compound en masse, in a highly correlated fashion. Unlike a superconductor, however, the electric CDW current often flows in a jerky fashion, much like water dripping from a faucet due to its electrostatic properties. In a CDW, the combined effects of pinning and electrostatic interactions likely play critical roles in the CDW current's jerky behavior, as discussed in sections 4 & 5 below.

<span class="mw-page-title-main">Collision cascade</span> Series of collisions between nearby atoms, initiated by a single energetic atom

In condensed-matter physics, a collision cascade is a set of nearby adjacent energetic collisions of atoms induced by an energetic particle in a solid or liquid.

The transport of heat in solids involves both electrons and vibrations of the atoms (phonons). When the solid is perfectly ordered over hundreds of thousands of atoms, this transport obeys established physics. However, when the size of the ordered regions decreases new physics can arise, thermal transport in nanostructures. In some cases heat transport is more effective, in others it is not.

<span class="mw-page-title-main">Local oxidation nanolithography</span>

Local oxidation nanolithography (LON) is a tip-based nanofabrication method. It is based on the spatial confinement on an oxidation reaction under the sharp tip of an atomic force microscope.

Leroy L. Chang was a Taiwanese-American experimental physicist and solid state electronics researcher and engineer. Born in China, he studied in Taiwan and then the United States, obtaining his doctorate from Stanford University in 1963. As a research physicist he studied semiconductors for nearly 30 years at IBM's Thomas J. Watson Research Center, New York. This period included pioneering work on superlattice heterostructures with Nobel Prize-winning physicist Leo Esaki.

<span class="mw-page-title-main">Coplanar waveguide</span> Type of planar transmission line

Coplanar waveguide is a type of electrical planar transmission line which can be fabricated using printed circuit board technology, and is used to convey microwave-frequency signals. On a smaller scale, coplanar waveguide transmission lines are also built into monolithic microwave integrated circuits.

<span class="mw-page-title-main">Franz Josef Giessibl</span> German physicist

Franz Josef Gießibl is a German physicist and university professor at the University of Regensburg.

Jean-Pierre Leburton is the Gregory E. Stillman Professor of Electrical and Computer Engineering and professor of Physics at the University of Illinois Urbana–Champaign. He is also a full-time faculty member in the Nanoelectronics and Nanomaterials group of the Beckman Institute for Advanced Science and Technology. He is known for his work on semiconductor theory and simulation, and on nanoscale quantum devices including quantum wires, quantum dots, and quantum wells. He studies and develops nanoscale materials with potential electronic and biological applications.

A. G. Unil Perera is a Sri Lankan-born American physicist with an assortment of research interests in experimental condensed matter physics, especially semiconductor infrared detectors and applications. He has authored over 200 publications covering a variety of disciplines inside. He is a Regents’ Professor of Physics at Georgia State University, in Atlanta, Georgia. After his basic Education in Sri Lanka, he obtained his doctoral degree in (applied) physics from the University of Pittsburgh under the supervision of Darry D. Coon. During his graduate research, he developed a detector, which can detect infrared (IR) radiation without the use of any amplifiers. (Solid State Electronics, 29, 929,. Then he introduced the concept of a two-terminal artificial neuron (International Journal of Electronics, 63, 61, , a parallel asynchronous processing based on artificial neurons , Neural Networks 2, 143, .( Phys. Rev. Lett., 58, 1139, . 

Aron Pinczuk was an Argentine-American experimental condensed matter physicist who was professor of physics and professor of applied physics at Columbia University. He was known for his work on correlated electronic states in two dimensional systems using photoluminescence and resonant inelastic light scattering methods. He was a fellow of the American Physical Society, the American Association for the Advancement of Science and the American Academy of Arts and Sciences.

Irving Philip Herman is an American physicist and the Edwin Howard Armstrong Professor of Applied Physics at Columbia University. He is an elected Fellow of the American Physical Society and of Optica, the former for "distinguished accomplishments in laser physics, notably the development and application of laser techniques to probe and control materials processing".

References

  1. 1 2 Tsu, Raphael (1960). The theory and application of the scattering matrix for electromagnetic waves (Ph.D.). Ohio State University. OCLC   946004753 via ProQuest.
  2. "Dr. Raphael Tsu, Ph. D." UNC Charlotte.
  3. Tsu, R.; Hernandez, J. G.; Chao, S. S.; Lee, S. C.; Tanak, K. (1982). "Critical Volume Fraction of Crystallinity for Conductivity Percolation in P-doped Si:F:H Alloys". Applied Physics Letters . 40 (6): 534. Bibcode:1982ApPhL..40..534T. doi:10.1063/1.93133.
  4. Tsu, R.; Isu, M.; Ovshinsky, S. R.; Polla, F. H. (1980). "Electroreflectance and Raman Investigation of Glow-Discharge Amorphous Si:F:H". Solid State Communications . 36 (9): 817. Bibcode:1980SSCom..36..817T. doi:10.1016/0038-1098(80)90019-8.
  5. Tsu, R. (1972). "High Technology in China". Sci. Am. 227 (6): 13.
  6. Esaki, L.; Tsu, R. (March 26, 1969). IBM Research Report RC2418. IBM Research Report (Report).
  7. Tsu, R.; Esaki, L. (1973). "Tunneling in a finite superlattice". Appl. Phys. Lett. 22 (11): 562. Bibcode:1973ApPhL..22..562T. doi:10.1063/1.1654509 . Retrieved October 28, 2022.
  8. Chang, L. L.; Esaki, L.; Tsu, R. (1974). "Resonant tunneling in semiconductor double barriers". Appl. Phys. Lett. 24 (12): 593. Bibcode:1974ApPhL..24..593C. doi:10.1063/1.1655067 . Retrieved October 28, 2022.
  9. Kawamura, H.; Tsu, R.; Esaki, L. (1972). "Disorder-Activated Acoustic Mode in Raman Spectrum of GaxAl1−xAs". Phys. Rev. Lett. 29 (20): 1397. Bibcode:1972PhRvL..29.1397K. doi:10.1103/PhysRevLett.29.1397 . Retrieved October 28, 2022.
  10. Tsu, R. (1964). "Phonon Radiation by Uniformly Moving Charged Particles in Piezoelectric Solids". J. Appl. Phys. 35 (1): 125. Bibcode:1964JAP....35..125T. doi:10.1063/1.1713018 . Retrieved October 28, 2022.
  11. Tsu, R.; Jha, S. S. (1972). "Phonon and Polariton Modes in a Superlattice". Appl. Phys. Lett. 20 (1): 16. Bibcode:1972ApPhL..20...16T. doi:10.1063/1.1653959.
  12. Tsu, Raphael; Datta, Timir (2008). Conductance and Wave Impedance of Electrons (pdf). Progress In Electromagnetics Research Symposium, Hangzhou, China, March 24–28. Hangzhou, China.