Development of High -Z Sensors for Pixel Array Detectors

Hybrid pixel detectors using silicon sensors have been successfully applied to experiments with X-rays, such as protein crystallography at synchrotrons. However, silicon has poor quantum efficiency at higher X-ray energies. To apply this hybrid pixel technology to experiments with harder X-rays, for example in materials science and medical imaging, it is necessary to use alternative semiconductors with higher atomic numbers (“high-Z semiconductors”). Currently, there are a few promising options. Cadmium Telluride offers high quantum efficiency at energies of 100keV and above, and the area and uniformity of the material available is improving. Gallium Arsenide is already available in large, uniform wafers, and new compensation techniques are being developed to overcome problems with its high trap concentration. Germanium is already available in large wafers of very high quality; however, it must be cooled during operation, and pixellation and bump-bonding techniques need to be developed for this material. In collaboration with Canberra, DESY is developing germanium pixel detectors using the Medipix3 readout chip. DESY is also developing large-area Medipix3 detector modules, which will be compatible with a variety of high-Z materials and silicon.