Study of Different Cadmium Telluride Materials Doped with V, Zn and Cl Grown by Vertical Bridgman Furnace and by THM
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Study of different Cadmium Telluride Materials doped with V, Zn and Cl grown by vertical Bridgman Furnace and by THM. Ch.Steer, L.Chibani, J.M.Koebel, M.Hage-Ali, P.Siffert CNRS Lab. Phase, F-67037 Strasbourg Cede;, France
ABSTRACT The properties of Cadmium Telluride are very sensitive to impurities. The growth method has also a strong impact on the material characteristics. Crystals grown by THM have good X-ray detector properties, while normal undoped Bridgman grown crystals do not detect. We have grown pure and doped samples by Bridgman and THM methods. As doping materials we used V, Zn and Cl, also in different combinations. The samples were characterized by several methods, including resistivity, TSC and nuclear detection measurements.
Introduction Cadmium telluride (CdTe) is a binary II-VI semiconductor compound with interesting characteristics for industrial applications. The high bandgap of about 1.5 eV and the high atomic number (Z=48,52) is interesting for room temperature gamma ray spectrometric detectors. The infrared properties are promising due to the compatibility with the wavelength of semiconductor lasers and fiber optic communications. Recently, the photorefractive properties of doped CdTe [1, 2] are investigated for telecommunication applications, this is a new and rapid growing market. In all applications, the electrical properties are very important. They vary strongly with the applied growth method and also with the impurity contents. We investigated in a comparative study on Traveling Heater Method (THM) and Bridgman (BM) grown crystals, pure or doped with Zn, V and Cl in different combinations.
Resistivity Measurements The samples for resistivity measurements are polished and etched. Gold contacts are deposited by electroless method. In table I the measurements are summarized. The resistivity of our pure, undoped CdTe is about 10i f0cm, regardless of the growth method. CdZnTe samples show comparable values. Doping by Vanadium pushes the resistivity to 10i... 109 0cm, however the samples show no or very bad detection properties. Chlorine doping gives 10" 0cm in BM and 10' 0cm in THM. But CdZnTe samples have still low resistivity around 10' f0cm in our conditions. The most interesting samples are CdTe:(V,Cl). They have a high resistivity, 10'... 1010 0cm, and the chlorine compensation gives acceptable nuclear detection properties.
Infrared Transmission Measurements The samples are annealed under Cd-pressure for 3 hours at 6500C and quenched to activate the dopants and impurities. Figure 1 shows the infrared transmission spectrum for several samples. We observed an absorption in the band of 7... 11pm correlated with the activated dopant concentration. The pure CdTe samples (THM, Krl6.1) show no increasing Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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Sample Kr28 Kr27 Kr25 Kr24 Kr23 Krl6 Kr14 Krl2
L647 L648 L653 L655 L656 T2090
T2077
meth. BM BM BM BM BM BM BM BM THM THM THM THM THM THM THM
dopant Cl,Zn Cl Zn V V
Zn Zn,Cl Zn,Cl Zn,C1 Zn
V V,Cl
conc.
sta
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