Energy resolution and transport properties of CdTe-Timepix-Assemblies

CdTe is a promising material for the detection of gamma- and X-rays as 1 mm thick CdTe sensors offer an absorption efficiency that is higher than 50 % for photon energies up to 120 keV. Therefore 1mm thick CdTe from Acrorad has been flip-chipped as the sensor material on a Timepix readout-electronics ASIC at the Freiburg Materials Research Center (FMF). The transport properties of the CdTe material are investigated by determining the mu tau-product of the charge carriers by illuminating the non-collecting electrode with alpha particles. The method commonly used to determine the mu tau-product for non-pixelated devices was adapted for the Medipix pixelated readout-electronics. The position of the alpha particles on the pixel matrix provides spatial information, which was used to create a mapping of the mu tau-product. The energy resolutions and the positions of the noise edge of two CdTe-Timepix assemblies, one with a pixel pitch of 110 x 110 mu m(2) and another one with a pixel pitch of 55 x 55 mu m(2) were investigated by performing a threshold scan of a (241)Am source. A comparison of the energy spectra obtained with the two assemblies with different pixel pitches confirms the strong dependence of charge sharing on the energy spectra, as expected.