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Register a new userRole of Zn in obtaining of semi-insulating CdZnTe crystals for ionizing radiations detectors
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Studies of n-CdZnTe crystals (photoluminescence, extrinsic photoconductivity, Hall effect, time-of-flight technique) have shown that the excess concentration of vacancies of cadmium (Vcd) is the main reason of low, as a rule, values of product of mobility to life time of holes (mhth). The reduction of the concentration of cadmium vacancies (decreasing of the intensity of near 1eV photoluminescence band and an intensity of the (0.9-1.3) eV extrinsic photoconductivity band) by annealing of the crystals at 600 C results in increasing of value of mhth. Influence of Zn on formation of the basic photoelectric properties of CdZnTe crystals has been explained by self-control of a concentration of cadmium vacancies Vcd due to addition of Zn results in formation of divacancies of metal, which in part dissociate and provide a crystal with necessary quantity of monovacancies for processes of complex formation. That makes process of obtaining of semi-insulating CdZnTe crystals less dependent from pressure Pcd in comparison with CdTe. However with the purpose of obtaining CdZnTe crystals with high value of mhth (i.e. with small concentration of the free vacancies of cadmium) it is necessary to control Pcd above the crystal at stages of its growth and annealing.
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The process of annealing of a CdTe:Cl ingot during its cooling after growth was studied. The annealing was performed in two stages: a high-temperature stage, with an approximate equality of chlorine and cadmium vacancy concentrations established at the thermodynamic equilibrium between the crystal and vapors of volatile components, and a low-temperature stage, with charged defects interacting to form neutral associations. The chlorine concentrations necessary to obtain semi-insulating crystals were determined for various ingot cooling rates in the high temperature stage. The dependence of the chlorine concentration [Cl+Te] in the ingot on the temperature of annealing in the high-temperature stage was found. The carrier lifetimes and drift mobilities were obtained in relation to the temperature and cadmium vapor pressure in the postgrowth annealing of the ingot.
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