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nanotimes
10-02 :: February 2010
News in Brief
Nanoelectronics //
A Step Towards Germanium
Nanoelectronics
T
he use of germanium instead of silicon as basic
The figure shows schematically the application of germa-
material of transistors would enable faster chips
nium in a CMOS (complementary metal oxide semicon-
containing smaller transistors. However, a number ductor) circuit. Note that germanium is only used in the
of problems still have to be solved. Transistors are
regions of source (S), drain (D) and channel (C). Source
produced using foreign atoms that are implanted into
and drain contain high concentration of foreign atoms
the semiconductor material so that it becomes partly
(dopants) which provide the excess of free electrons
(n+ regions) or holes (p+ regions). © FZD, Germany
conducting. As this production step damages the ma-
terial, it has to be repaired by subsequent annealing.
So far it has not been possible to produce large-scale nium was performed in close collaboration with
integrated transistors of a specific type (NMOS) using colleagues from the Belgian microelectronics center
germanium. The reason: phosphorus atoms are stron- IMEC in Leuven and from the Fraunhofer-Center for
gly redistributed within the material during annea- Nanoelectronic Technologies (CNT) in Dresden.
ling. Two novel technique overcome this dilemma. C. Wündisch, M. Posselt, B. Schmidt, V. Heera, T. Schu-
mann, A. Mücklich, R. Grötzschel, W. Skorupa, T. Cla-
Physicists from the German research center Dres- rysse, E. Simoen, H. Hortenbach: Millisecond flash lamp
den-Rossendorf (FZD) applied a special annealing annealing of shallow implanted layers in Ge, In: Applied
method that enables repairing the germanium cry- Physics Letters, Vol. 95(2009), Issue 25, December 23,
stal and yields good electrical properties without 2009, Article 252107, DOI:10.1063/1.3276770:
the diffusion of phosphorus atoms. The germanium

http://dx.doi.org/10.1063/1.3276770
samples were heated by short light pulses of only a
few milliseconds. This period is sufficient in order to H. Bracht, S. Schneider, J. N. Klug, C. Y. Liao, J. Lundsg-
restore the crystal quality and to achieve electrical aard Hansen, E. E. Haller, A. Nylandsted Larsen, D. Bou-
activation of phosphorus, but it is too short for the geard, M. Posselt, C. Wündisch: Interstitial-Mediated Dif-
spatial redistribution of the phosphorus atoms. The fusion in Germanium under Proton Irradiation, In: Physical
light pulses were generated by the flash lamp equip- Review Letters, Vol. 103(2009), Issue 25, December 18,
ment which was developed at the research center 2009, Article 255501 [4 pages], DOI:10.1103/PhysRev-
FZD. Analysis of the electrical and structural proper- Lett.103.255501:
ties of the thin phosphorus-doped layers in germa-

http://dx.doi.org/10.1103/PhysRevLett.103.255501