Inhomogeneous resistivity and its effect on CdTe- and CdZnTe-based radiation detectors
Jakub Zázvorka (Institute of Physics, Charles University, Prague, Czech Republic)

Cadmium telluride and its zinc compounds are the materials of choice for room temperature applications in high energy spectroscopic radiation detectors. The development of the final device is influenced by a big variety of parameters, including material impurities and defects, homogeneity and material surface treatment. Fabrication processes, detector parameters and physical effects influencing their spectroscopic resolution and performance are intensively studied at Charles University. One of the disadvantages of the CdTe material family is the relative low yield vs. cost ratio in crystal growth. This issue is the result of a complex and volatile stoichiometry of the material and requires material doping to achieve high resistivity material for a suitable signal-to-noise ratio of the final detector. After the crystal growth, even within a monocrystalline grains, an inhomogeneous resistivity distribution is frequently observed. This phenomenon is caused by an inhomogeneous defect and impurity distribution and affects the charge transport and charge collection in the final detector device. Therefore CdTe detector devices prepared from novel growth methods have to be studied and their bandgap structure (including deep energetic levels induced by defects), charge transport and collection properties have to be characterized in order to find a suitable and optimized detector development process.
The characterization methods employed for this systematic study included contactless resistivity, photoconductivity, photoluminescence, electro-optical Pockels effect, Hall effect, ellipsometry, transient currents and charge collection measurements.