Willy Werner van Roosbroeck

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Willy Werner van Roosbroeck (* 1913 in Antwerp ; † June 22, 1995 in Summit (New Jersey) ) was an American physicist. His most important merit are his theoretical contributions to semiconductor solid state physics: to charge carrier transport, to radiative recombination and to relaxation semiconductors .

life and work

Van Roosbroeck came to the USA from Belgium with his parents in 1916. In 1934 he received an AB (Bachelor of Arts) and in 1937 an MA (Master of Arts) in physics, both from Columbia University in New York. All his professional life, from 1937 to 1978, van Roosbroeck was a scientist at the Bell Telephone Lab, first in New York and from 1941 in Murray Hill (New Jersey) . The Bell Telephone Lab later went into the AT&T Bell Laboratories . In the early days he worked on high frequency resistors carbon films as well as the theory of thermistor - bolometers , a variant of radiation sensors for the infrared range.

Load carrier transport

In 1948 he moved to the physics department of Bell Labs and turned to problems in solid state physics. On the theory of electron-hole transport in germanium, van Roosbroeck wrote a much-cited article, the core of which is a system of equations for determining the charge carrier flows due to drift and diffusion. The drift diffusion model defined by the van Roosbroeck equations is still the starting point of every semiconductor system calculation today.

Radiant recombination

Later, together with W. Shockley , he developed a semi-classical model for radiative recombination from the principle of detailed equilibrium (i.e. the same probability for an elementary process and its reversal) : the rate for spontaneous radiative recombination is calculated within the van Roosbroeck-Shockley model under equilibrium conditions from the band gap energy, the absorption coefficient and the refractive index.

Relaxation semiconductors

From around 1960 onwards, van Roosbroeck mainly investigated semiconductors in operating states in which the dielectric relaxation time is longer than the recombination lifetime of the free charge carriers: then, with regard to the space charge density, the quasi-neutrality can be disturbed for a long time, which basically entails different characteristics of the charge transport. He recognized this case as a new type of semiconductor behavior and coined the term relaxation case or relaxation semiconductor for it. If the above time comparison turns out the other way round, the recombination semiconductors, which have been known for some time, show the typical semiconductor properties in the range of a low electrical resistance at room temperature. The classification into recombination or relaxation semiconductors does not apply absolutely to materials, but always relates to the material in question at a given temperature and possible injection of charge carriers. Relaxation semiconductors have a significantly higher electrical resistance than recombination semiconductors, and they include u. a. some representatives of semiconductors with a large band gap, of semi-insulating compound semiconductors (e.g. GaAs at room temperature), of amorphous semiconductors and of high-purity semiconductors at very low temperatures: z. B. changes high-purity silicon from the recombination semiconductor (at room temperature) to the relaxation semiconductor (below 20 K). The first detailed experimental confirmation of the electrical characteristics predicted by van Roosbroeck in the relaxation case was achieved in collaboration with Hans J. Queisser and H. Craig Casey Jr using measurements on a GaAs - pn junction .

literature

  • H.-J. Queisser: The relaxation case, a new area in semiconductor physics . In: Physics in Our Time . tape 4 , no. 3 , 1973, p. 78-81 , doi : 10.1002 / piuz.19730040303 .
  • NM Haegel: Relaxation semiconductors: In theory and in practice . In: Appl. Phys. A . tape 53 , no. 1 , 1991, p. 1-7 , doi : 10.1007 / BF00323427 .
  • H. Gajewski: Analysis and numerics of charge transport in semiconductors . In: GAMM messages . tape 16 , no. 1 , 1993, p. 35-57 .
  • James Josenhans: Willy Werner van Roosbroeck . In: Physics Today . March, 1996, pp. 126-27 .
  • Stephen J. Fonash: Solar Cell Device Physics . Academic Press (imprint of Elsevier), Amsterdam 2010, ISBN 978-0-12-374774-7 , pp. 335-37 (chap. E.1) .

Individual evidence

  1. ^ W. van Roosbroeck: Theory of the flow of electrons and holes in germanium and other semiconductors . In: Bell System Techn. Journal . tape 29 , no. 4 , 1950, p. 560-607 , doi : 10.1002 / j.1538-7305.1950.tb03653.x .
  2. ^ W. van Roosbroeck and W. Shockley: Photon-Radiative Recombination of Electrons and Holes in Germanium . In: Phys. Rev . tape 94 , no. 6 , February 19, 1954, p. 1558-60 , doi : 10.1103 / PhysRev.94.1558 .
  3. ^ Fred Schubert: Light Emitting Diodes . Cambridge University Press, 2006, ISBN 978-0-521-86538-8 , pp. 50–54 (Section 3.2) .
  4. ^ W. van Roosbroeck: Current-Carrier Transport with Space Charge in Semiconductors . In: Phys. Rev . tape 123 , no. 2 , March 9, 1961, p. 474-90 , doi : 10.1103 / PhysRev.123.474 .
  5. ^ W. van Roosbroeck and HC Casey, Jr .: Transport in Relaxation Semiconductors . In: Phys. Rev . tape 5 , no. 6 , May 13, 1970, pp. 2154-75 , doi : 10.1103 / PhysRevB.5.2154 .
  6. ↑ BT Cavicchi and NM Haegel: Experimental Evidence for Relaxation Phenomena in High-Purity Silicon . In: Phys. Rev. Lett . tape 63 , no. 2 , May 22, 1989, pp. 195-98 , doi : 10.1103 / PhysRevLett.63.195 .
  7. ^ HJ Queisser, HC Casey, Jr., and W. van Roosbroeck: Carrier Transport and Potential Distributions for a Semiconductor pn Junction in the Relaxation Regime . In: Phys. Rev. Lett . tape 26 , no. 10 , December 21, 1970, pp. 551-554 , doi : 10.1103 / PhysRevLett.26.551 .
personal data
SURNAME van Roosbroeck, Willy Werner
BRIEF DESCRIPTION American physicist
DATE OF BIRTH 1913
PLACE OF BIRTH Antwerp
DATE OF DEATH June 22, 1995
Place of death Summit (New Jersey)