Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 7: Instrumentation und Anwendungen
HK 7.3: Vortrag
Freitag, 4. März 2005, 15:00–15:15, TU MA042
Charge carrier mobility in segmented large volume HPGe detectors — •B. Bruyneel, P. Reiter, J. Eberth, and D. Weisshaar — IKP, Universität zu Köln
γ-ray tracking in future HPGe arrays
like AGATA will rely on pulse shape analysis of multiple
γ-interactions. Therefore, an accurate description of
electron and hole mobility as a function of the electric field
strength is needed. Preamplified signals from a 12-fold segmented
MINIBALL detector [1] were processed using digital XIA electronics
[2]. For the electrons the whole crystal surface was scanned
yielding 336 detector responses with a collimated 241Am
source.
Anisotropy and crystal geometry cause considerable rise time
differences in pulse shapes ranging up to 30% at the front side
of the detector. Pulses of direct and transient signals are very
well reproduced by weighting field calculations.
Exploiting the segmentation a precise measurement of the hole
drift anisotropy - a 10% rise time effect - was performed for the
first time with 356 keV γ-rays from a 133Ba source.
The measured angular dependence of the rise times is caused by the
crystal orientation and geometry, changing field strength and
space charge effects. For the hole mobility in Ge semiconductors
an applicable theoretical description is missing. Hence, a model
based on the drifted Maxwellian hole distribution was developed
for the hole drift anisotropy using the experimental velocity
along the crystal axis as parameters.
∗ Supported by the German BMBF(06 K-167).
[1] P.Reiter et al., Nucl. Phys. A701 209 (2002)
[2] DGF-4C User’s Manual, XIA, http://www.xia.com