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 (~ 10 10 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 Cdannealing of the samples is discussed. Characterization of the obtained crystals is described. The behaviour of the preliminary detectors is shown.

CdMnTe offers several potential advantages over CdZnTe as a roomtemperature gamma-ray detector, but many drawbacks in its growth process impede the production of large, defect-free single crystals with high electrical resistivity and high electron lifetimes. Here, we report our findings of the defects in several vanadium-doped as-grown as well as annealed Cd 1Àx Mn x Te crystals, using etch pit techniques. We carefully selected single crystals from the raw wafer to fabricate and test as a gamma-ray detector. We describe the quality of the processed Cd 1Àx Mn x Te surfaces, and compare them with similarly treated CdZnTe crystals. We discuss the characterization experiments aimed at clarifying the electrical properties of fabricated detectors, and evaluate their performance as gamma-ray spectrometers.

There are few previous data on the magnetothermoelectric properties of degenerate semiconductors. Although magnetic quantum oscillations in the thermopower have been previously studied, quantitative, or even semiquantitative agreement with theory was not achieved. We have developed a theoretical model allowing a quantitative description of both the oscillatory and nonoscillatory parts of the thermopower tensor S, and have studied its validity in an experimental system. For the experiments we have chosen a high mobility sample of HgSe:Fe (nϭ4.6ϫ10 24 m Ϫ3 ), and have measured both of the independent components of S in a transverse magnetic field B of р8 T at temperatures 1 KϽTϽ60 K, together with the longitudinal and Hall resistivities and the thermal conductivity. Our model predicts that the transverse component S yx is not affected by phonon drag, and all our data are in agreement with this. The absolute value of the nonoscillating part of S yx depends linearly on T consistent with domination by diffusion. We observe large oscillations in S yx which exhibit a phase shift of /2 relative to the resistivity oscillations. By including elastic electron scattering in the diffusion theory we obtain excellent quantitative agreement for both the oscillations and the smooth background under all conditions of B and T, including the observed phase shift of /2. In contrast to S yx , the longitudinal component S xx shows a large contribution from phonon drag over most of the temperature range. S xx exhibits quantum oscillations similar to S yx , but these are found to be in phase with those in the resistivity and are far too large to be explained by diffusion in any available model. Instead, they are well described by oscillations in electron-phonon scattering which modulates phonon drag in much the same way as is observed in twodimensional systems. Small oscillations are also observed in the lattice thermal conductivity and their magnitude is shown to be consistent with the same phonon-electron scattering being responsible. Our analysis demonstrates that the study of the thermopower is a powerful tool in the understanding of both the elastic ͑through S yx ) as well as the inelastic ͑through S xx ) scattering of electrons in degenerate semiconductors.

No abstract