Current research / employment

Short abstract about IMPRS PhD project:

The development of new advanced X-ray detectors was the goal of of my phd project. The focus is set on the signal generation inside the sensor volume of a direct converting semiconductor detector. Incoming particles interact with the sensor material and generate clouds of electron hole pairs. These pairs get separated by an applied bias voltage. The motion of the charge clouds is simulated with a finite element programme taking into account the drift and diffusion.

Mirror charges are induced on the electrodes which move due to the motion of the charge cloud. The motion of the induced mirror charges leads to the signal that is detected. The transient calculation of the signals is based on Ramo's theorem. The efficient adjoint formulation of the induction solution is adjusted to doped materials, as for example the electric bias field and hence the motion of the charge cloud is changing with the doping level. The effect of the doping of the material on the signal shape is shown together with influences of different voltages and pixel geometries.

Smaller pixels and higher bias voltages can lead to shorter signals which is preferable for high flux measurements. Possible count rate improvements are limited by electric break through, high dark current across the sensor layer and charge sharing. Another option to shorten the signals is the use of steering grid electrodes which modify the electric and the weighting field. This results in shorter signals and thus in a higher possible rate.

Current employment: Siemens

Publications B. Kreisler, J. Durst, T. Michel, G. Anton, Generalised adjoint simulation of induced signals in semiconductor X-ray pixel detectors, JINST, 3, P11002, (2008)

T. Michel, G. Anton, M. Böhnel, J. Durst, M. Firsching, A. Korn, B. Kreisler, A. Loehr, F. Nachtrab, D. Niederlöhner, F. Sukowski, P. Takoukam Talla, A fundamental method to determine the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) for a photon counting pixel detector, NIM A, 568(2), 799-802, (2006)