Gamma-Ray Response of Semi-Insulating CdMnTe Crystals
Semi-insulating Cd0.9Mn0.1Te:In crystals are grown by vertical Bridgman method. The segregation coefficient of Mn in CdTe is nearly 1 so that all the CdMnTe samples obtained from one ingot have nearly a same Mn composition. Also sulfur-based passivation effectively prevent the formation of Te-oxide but large amount of Mn exist as a MnO on the CdMnTe surface. The resistivity of CdMnTe samples are low 1010 Omegacm and well resolved 241Am gamma peaks are seen for all detectors. The difference in spectral response can be attributed to the effect of excess Te and conductivity change due to over-compensation induced by indium segregation in CdMnTe. The mobility-lifetime products evaluated from the dependence of peak location on the bias voltage are 1 times 10-3 cm2/V. The higher mobility-lifetime products in our CdMnTe crystals than other previous reports are assumed due to minimization of impurity contents in MnTe by several zone refining process.
Impurities Behaviors in Indium Iodide Materials
Environmentally friendly 99.998%-pure indium iodide (InI), one candidate materials for the room-temperature operating radiation detector, was purified more than 250 times using the zone-refining method to reduce the impurities. Segregation coefficient of major positive and negative impurities of the purified InI ingot was analyzed using time-of-flight secondary ion mass spectroscopy. Electrical and spectroscopic properties of the purified Pd/InI/Pd detector were also determined. Planar Pd/InI/Pd detector showed the 59.5-keV gamma peak of Am-241 clearly. However, low-energy gamma peaks were buried in the noise. Mechanical or electrical degradation under an ambient condition was not observed for six months. Electrical resistivity and electron mobility-lifetime product of the multiple-refined InI were <inline-formula> <tex-math notation="LaTeX">$4\times 10^{11}\,\,\Omega \cdot \textrm {cm}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$1.3\times 10^{-3}\,\,\textrm {cm}^{2}/\textrm {V}$ </tex-math></inline-formula>, respectively.
Zinc segregation in HPB grown nuclear detector grade Cd1−xZnxTe
CZT ingots have been grown by the high pressure Bridgman technique and their zinc concentration has been measured by X-ray fluorescence and PIXE on samples cut at different growth positions. The zinc concentration map has been traced for several wafers showing strong discrepancies along the explored area. The segregation coefficient has been calculated from the experimental data taking a directional freezing model. A very good fitting with experimental values is obtained especially for the PIXE results. Some detectors have been manufactured from the wafers and tested in nuclear detection. It is shown that pair creation energy is modified and that the saturation curve is modified from the head to the tail of the ingot.