Characterization of CdTe:Zn:V crystals grown under microgravity conditions
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V. Babentsovb) Kristallographisches Institut, Universitat Freiburg, Hebelstrasse 25, D-79104 Freiburg, Germany
J.L. Castan˜o Departamento Fisica Aplicada, Universidad Auto´noma de Madrid, 28049 Madrid, Spain
M. Fiederle, T. Feltgen, and K. Benz Kristallographisches Institut, Universitat Freiburg, Hebelstrasse 25, D79104 Freiburg, Germany
E. Dieguez Departamento Fisica Aplicada, Universidad Auto´noma de Madrid, 28049 Madrid, Spain (Received 13 March 2002; accepted 20 August 2002)
CdTe:Zn:V crystals grown by the seeded Bridgman method in microgravity conditions during the STS95-Spacelab-AGHF-1 mission and in the ground laboratory (l-g) were analyzed and compared. The results obtained clearly show that the structural quality of the space crystal is better. Density of inclusions, concentration of dislocations, and presence of stresses are lower in the microgravity-grown (-g) crystal. The l-g crystal contains twins and grains from the beginning of the growth process, that is, from the near-seed region. In general, the concentration of inclusions and amount of segregated impurities on the l-g crystal are larger than in the -g crystal. X-ray rocking curves and low-temperature photoluminescence spectra demonstrate the relatively high quality of both crystals on a microscale at the beginning of the growth and show that the l-g conditions were worse at the end. The results of this investigation demonstrate a positive role of contactless growth and -g conditions in the melt in suppressing the creation of inclusions and dislocations.
I. INTRODUCTION
CdTe crystals are used in photorefractive devices and in radiation detectors able to work at room temperature. For these purposes crystals with high quality and crystallinity, as well as low-density dislocations, are required. Different growth techniques have been used for growing CdTe from the liquid or vapor phase. The Markov method of growth from the vapor phase gives crystals with high quality since the contact with the ampoule is avoided and a low growth temperature is used, but is still not commercially used.1 The conventional Bridgman method is currently more available, but it suffers from the melt convection flow and the contact with the walls of a quartz ampoule. Gravity plays an important role; it is
a)
Address all correspondence to this author. e-mail: [email protected] b) Permanent address: Institute for Semiconductor Physics, Pr. Nauki, 45 Kiev, 252028, Ukraine J. Mater. Res., Vol. 17, No. 12, Dec 2002
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responsible, for example, for the thermal convection due to the different density of the melt at different temperature, and of the hydrostatic pressure. In Larson’s experiments in microgravity-grown (-g) conditions, during the USMP1 and 2 missions,2 single (Cd,Zn)Te crystals without grains and twins, which had dislocation density and residual stresses several orders of magnitude lower than in the crystals grown in terrestrial conditions, were obtained. For these reasons, conditions of microgravity
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