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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P406
Internal drift effects explaining anomalous diffusion profiles of Ag in CdTe
Frank Wagner 1 , Jörg Kronenberg 1 , Herbert Wolf 1 , Manfred Deicher 1 ,
Karl Johnston 1 , Thomas Wichert 1 , ISOLDE Collaboration 2
1 Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany –
2 CERN, CH-1211 Geneva 23, Switzerland
Anomalous concentration profiles have been observed upon diffusion of Ag in CdTe
[1]. The diffusion experiments were performed with the radiotracers 111 Ag implanted
at ISOLDE into one side of a typically 800 µm thick CdTe crystal at a depth of about
30 nm. The resulting diffusion profiles of Ag extending over the whole crystal critically
depend on the respective external conditions during diffusion and on the sample
pre-treatments (see figure): After diffusing the Ag dopant into the CdTe crystal at 800
K (60 min) under Cd pressure or vacuum the symmetrical concentration profiles show
depletion layers of 100 or 300 µm below the surfaces of the crystal, whereby the depletion
layers are much stronger pronounced in case of diffusion under Cd pressure. In
contrast, the Ag concentration is increased at the surface and decreased in the interior
of the crystal if the diffusion is performed under Te pressure. These anomalous Ag profiles
are well described within a model based on an interaction of the Ag dopant atoms
with the intrinsic defects of the Cd sublattice of CdTe taking into account the charge
states of all participating defects. It turns out that the diffusion of Ag is significantly
affected by an internal drift due to the electric field generated by the distribution of the
charged defects. In addition, the influence of Cu, Au, and In on the diffusion of Ag
in CdTe was investigated. Thus, evaporating a thin Cu layer on the 111 Ag implanted
side of a CdTe single crystal and subsequent annealing at 550 K for 30 min effects that
most of the Ag atoms were detected in a thin layer of only a few µm at the back of a
500 µm thick crystal.
This work has been supported by the Bundesministerium für Bildung und Forschung
(BMBF) under Contract Nos. 05 KK1TSB/5 and CZE 03/002.
[1] H. Wolf, F. Wagner, Th. Wichert, and ISOLDE Collaboration, Phys. Rev. Lett.
94 (2005) 125901.