Search of a characterisation methodology of CdTe/CZT wafers for imaging

The homogeneity of the semi-insulating CdTe/CZT crystals will determine the capacity of these semiconductors to be used in pixelized imaging applications using gamma- and X-rays. It appears that the smaller the pixel unit size, the better the material uniformity has to be. Fast characterization methods become therefore, imperative to keep the production costs in industry acceptable. The goal of the present study is to evaluate two experimental methods in their ability to fulfill in a quick and routine manner the material properties: RESISTIVITY MAPPING: a contactless time dependent charge measurement (TDCM) method was used for mapping large scale wafers with spatial resolution of 1.0 mm² in an automatic set-up. It gives very good reproductibility for resistivities higher than 10⁶ Ohm cm and displays full scale image of the resistivity distribution. - INFRARED TRANSMISSION MAPPING: allows the analysis of Te inclusions and an adapted software gives directly the distribution of the precipitate sizes. Samples of THM grown CdTe crystals have been investigated as grown and after various thermal treatments and the pixelized detectors produced from these wafers were tested using a ⁵⁷Co radiation source.