HiZPAD (Hi-Z sensors for Pixel Array Detectors)

A range of heavy semiconductors such as GaAs, Ge and CdTe are available, but each material has strengths and weaknesses. The aim of the HiZPAD collaboration is to develop these materials for use at synchrotrons. As part of this collaboration, DESY have tested CdTe-based pixel detectors.

Image of diffuse scattering around the Bragg peak of LiMnPO4, taken with the CdTe detector. The logarithmic scale shows the number of counts accumulated in each pixel.

CdTe pixel detector with 256 by 256 55µm pixels, read out by a Medipix2 chip

DESY are members of the HiZPAD consortium, which is an ESRF-led project funded by the EU through ELISA. The aim of the project is to foster the development of high-Z sensors for high-energy synchrotron beamlines, and the consortium is focusing in particular on cadmium telluride (CdTe) and cadmium zinc telluride (CZT) sensors. Due to their extremely high atomic numbers, these sensors are particularly suitable for experiments at 100 keV and above, where even Ge and GaAs sensors have lower efficiency.

Wafers of CdTe and CZT are already commercially available, and are being used in single-element sensors and small arrays. However, these wafers are limited to 3” diameter, often have inhomogeneities, and are difficult to handle due to their fragility, all of which make it more difficult to produce good pixel sensors. The consortium have commissioned CdTe and CZT pixel sensors from different manufacturers bond to a variety of X-ray detector readout chips (Medipix, Pilatus, XPAD).

Single-chip CdTe sensors bonded to Medipix2 have been tested at DORIS BW5. Although the chip has some inactive pixels due to sensor defects, it is nevertheless useful due to its high efficiency, single-photon-counting capability and relatively fast readout. For example, the detector has been used to measure diffuse scattering from a LiMnPO4 sample.

Project Leader: Heinz Graafsma