Raphael Tsu

Raphael Tsu
Tsu in 2019
Other nameRay Tsu
Education
Known forResonant tunneling diode
AwardsInternational Prize for New Materials (1985)
Scientific career
FieldsElectrical engineering
Workplaces
ThesisThe theory and application of the scattering matrix for electromagnetic waves (1960)
Robert Kouyoumjian

Raphael Tsu is an American electrical engineer who is Professor Emeritus of Electrical and Computer Engineering at the University of North Carolina at Charlotte.

Education

Tsu earned a Bachelor of Science in Engineering from the University of Dayton in 1956. He completed his graduate studies at Ohio State University, where he received a Master of Science in 1957 and a Doctor of Philosophy in 1960. His doctoral advisor at Ohio State was Robert Kouyoumjian.

Career

After several years working as a member of the technical staff at Bell Telephone 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], and providing experimental proof of the existence of an intermediate order. 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. 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.

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, 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 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.

Recognition

Memberships

Year Organization Type Ref.
1980 American Physical Society Fellow

Awards

Year Organization Award Citation Ref.
1985 American Physical Society International Prize for New Materials "For his conception of artificial semiconductor superlattices and his recognition that such structures have realizable and would have novel electronic properties. His sustained experimental and theoretical efforts have helped lead the way to versatile new materials and technologies."

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 .

References

  1. 1 2 "Dr. Raphael Tsu, Ph.D." University of North Carolina at Charlotte. Archived from the original on March 5, 2026. Retrieved October 28, 2022.
  2. ↑ Tsu, Raphael (1960). The theory and application of the scattering matrix for electromagnetic waves (Ph.D. thesis). OCLC 946004753. ProQuest 301850387.
  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): 13–17. JSTOR 24922932.
  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. Progress In Electromagnetics Research Symposium, Hangzhou, China, March 24–28. Hangzhou, China. Archived from the original (pdf) on August 3, 2010. Retrieved April 26, 2013.
  13. ↑ "APS Fellows archive". American Physical Society. Retrieved July 30, 2025.
  14. ↑ "James C. McGroddy Prize for New Materials". American Physical Society. Retrieved October 8, 2023.