Is the (Cd,Mn)Te crystal a prospective material for X-ray and γ-ray detectors?



To answer the title question – the technology and properties of the (Cd,Mn)Te crystals is discussed as compared with those of the more commonly used (Cd,Zn)Te crystals. The composition homogeneity of the large single crystals of the ternary compound seems to be easier to achieve in the case of (Cd,Mn)Te because the segregation coefficient of Mn in CdTe is negligible with respect to that (approx. 1.3) of Zn. Only 15% of MnTe has to be added to CdTe to reach the best for the detector application value of the energy gap (in the range 1.7–2.2 eV), while the necessary amount of ZnTe is over 30%! This is because the composition dependence of the CdTe energy gap is for Mn twice as strong as for Zn. Using a smaller amount of the second cation diminishes many alloying-related problems. Dopant-free as grown (Cd,Mn)Te crystals are of p-type, which is related to the Cd vacancies acting as acceptors. The number of vacancies can be reduced by the post-growth annealing in the Cd vapours and the high (∼1010 Ωcm) resistivity, required for good detectors, can be obtained by doping with donors. The technology of the (Cd,Mn)Te crystals, undoped and compensated in the very large range of concentrations, and Cd-annealing of the samples is discussed. Characterization of the obtained crystals is described. The behaviour of the preliminary detectors is shown. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)