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.
Investigation of the Charge Collection Efficiency of CdMnTe Radiation Detectors
This paper presents the growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe) crystals grown by the vertical Bridgman technique. The 10 × 10 × 1.9 mm3 samples have been fabricated, and the charge collection properties of the CdMnTe detectors have been measured. Alpha-particle spectroscopy measurements have yielded an average charge collection efficiency approaching 100%. Ion beam induced charge (IBIC) measurements have been performed by raster scanning focused 5.5 MeV 4He beams onto the detectors. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of Te inclusions within the detector bulk, and the reduction in charge collection efficiency in their locality has been quantified. It has been shown that the role of Te inclusions in degrading charge collection is reduced with increasing values of bias voltage. IBIC measurements for a range of low biases have highlighted the evolution of the charge collection uniformity across the detectors.
Tellurium antisites in CdZnTe
The n-type conduction of CdTe and Cd0.96Zn0.04Te crystals grown from melts with excess tellurium indicates that the origin of the donors with an energy level at 0.01 eV below the conduction band are most likely singly ionized tellurium antisites instead of cadmium interstitials. Based on this model, the deep level at 0.75 eV below the conduction band is therefore doubly ionized tellurium antisites. After increasing the zinc content over 7%, CdZnTe turns to p-type. The conduction type variation of CdZnTe crystals as a function of zinc contents is explained by the compensation between the donors of Te-antisites and the acceptors of Cd vacancies. High resitivity Cd0.9Zn0.1Te crystals are produced by compensating the p-type crystals with indium at a low doping level of 1- 5x1015 cm-3. At room temperature, the high yield CdZnTe radiation detectors can resolve the six low energy peaks from the Am241 source, a performance comparable to the best reported CdZnTe detectors.