Resistivity and mu-tau imager for automatic characterization of semiconductor materials

Despite intensive research for the improvement of the quality of II-VI crystals, until now no clear method permits to determine quickly the performance of final detector, directly on the as-grown crystal or on the wafers. This situation induces excess cost, which hinders the development of detectors based on these binary and ternary semiconductors. The homogeneity of the semi-insulating crystals will determine the capacity of these semiconductors to be used in gamma and X- rays detectors for imaging in medical, spatial and industrial applications. It appears, that the smaller the pixel unit size is, the better the material uniformity has to be. Fast characterization and non destructive methods become, therefore, imperative to keep the production costs in industry acceptable. The previously developed innovative contactless equipment for the mapping of resistivity of the wafers before contacts are deposited has become of great interest with a rather large domain of resistivity (from 10⁶ up to 10¹² Ohm cm). We have introduced an additional contactless wafer mu-tau imaging of electrons on the same wafer automatically. The principle is based on a localized excitation of the wafer without any electrical contact and a particular use of the Hecht relation. In this paper, the main features of this new instrument will be presented and the results obtained on different materials CdTe, CdZnTe or CdMnTe presented and discussed. Very satisfying agreement has been observed between the results obtained with the new system and conventional methods based on the I-V and alpha spectroscopic measurements of detectors produced from these materials.