CdTe:Cl and CdTeSe:Cl Single Crystals Application for Radiation Detectors
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CdTe:C1 AND CdTeSe:CI SINGLE CRYSTALS APPLICATION FOR RADIATION DETECTORS B.K. MEYER, D.M. HOFMANN, W. STADLER, M. SALK+, C. EICHE+, AND K.W. BENZ+ Technical University of Munich, Physik-Department E 16, D-8046 Garching, Germany +Kristallographisches Institut, University Freiburg, D-7800 Freiburg, Hebelstr. 25, Germany ABSTRACT We report on electrical and optical properties of vertical Bridgman grown Cl-doped CdTe including the ternary compositions Cd 0 .9 Zn0 .1Te and CdTe0 .9 Se0 .1 with respect to application as a radiation detector. Based on Hall effect measurements, photoinduced current spectroscopy (PICTS) and photoluminescence we infer that high resistive material with good performance is controlled by deep level defects. The resistivity is calculated as a function of the shallow acceptor concentration (Cl-Acenters) with the conclusion that a deep donor state at mid gap must be present. I. INTRODUCTION High resisitive CdTe is one of the key materials for room-temperature radiation detectors. In vertical Bridgman grown c stals this is usually achieved by Chlorine (Cl) doping in the range from 1017 up to 109 cm"3 . It results in the formation of shallow isolated Cl-donors and simultaneously in the creation of Cl-related acceptors (Acenters, a Cd-vacancy paired off with a nearest neighbour CITe), single acceptors in CdTe. In this report we combine Hall effect measurements, PICTS, magnetic resonance and photoluminescence experiments to conclude about the compensation action of A-centers with respect to high resistivity. U1.EXPERIMENTAL The vertical Bridgman-technique (without Cd overpressure) was used to grow CdTe, Cd0 .9 Zn0 . 1Te and CdTe 0 .9 Se0 .1 crystals. The materials were synthesized from the elements Cd and Te, 7N purity, and Zn or Se, 6N purity, all from Nippon Mining. Part of the crystals were doped by adding CdCl 2 or TeCI4 up to concentrations of 2*1019 cm 3 to the starting materials. Doping by Cl gas was done in a specially designed dosage apparatus. The weight corresponding Cl gas quantities were condensed at LN2 temperatures into the synthesis ampoule. Both doping techniques assume complete incorporation of the dopant. The synthesis and the crystal growth were performed in the same sealed quartzglass ampoule. After a homogenization time of 6 h the ampoule was moved with the pulling rate of 1 mm/h (24 mm/d). Afterwards the ampoule was cooled down with the cooling rate of 20*C/h. The electrical properties of the grown crystals are shown in tab.1. As in CdTe, high resistive materials were obtained by Cl doping of the ternary crystals. CdTe:C1 and Cd 0 .9 Zn0 .1 Te:Cl crystals were always p-type under the experimental conditions
Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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described above. In contrast, the conductivity of the CdTe 0 .9 Se0 . 1:CI was n-type in all investigated samples. This might be a first hint of the n-type behavior of CdSe. The highest resistivity was achieved in the case of CdTe0 .9 Se0 .1 :CI, the lowest in Cd 0 .9 Zn0 .1 . The variation of the
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