Abstract
Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.
Highlights
IntroductionX-rays of (Cd, Zn)Te (CZT) make this material suitable for developing highly efficient radiation detectors
The electrical properties, room temperature operability and absorption efficiency forX-rays of (Cd, Zn)Te (CZT) make this material suitable for developing highly efficient radiation detectors
The Laue patterns of two spots at Position 1 in the seed and Position 3 in the grown crystal (Figure 1a) demonstrate that the angels between these two area surfaces and (111) plane are 30.81◦ and 30.76◦, respectively. This and Position 3 in the grown crystal (Figure 1a) demonstrate that the angels between thes two area surfaces and (111) plane are 30.81° and 30.76°, respectively. This result sugges that the two grains share the same orientation, and the seeding process is successful
Summary
X-rays of (Cd, Zn)Te (CZT) make this material suitable for developing highly efficient radiation detectors. In a THM system, growth occurs from a Te-rich solution zone at a temperature lower than the melting point, which brings the benefits of lower defects and contaminations. Another main advantage of THM is a high compositional uniformity of the regrown crystal because THM establishes a steady state. The performance, uniformity and efficiency of detector devices are still limited by the compositional inhomogeneities and structural defects, such as Te inclusions, dislocations, grain/subgrain boundaries, twins and even cracks in the material [7,8,9]. The associated dislocations may increase further charge trapping by accumulating secondary phases and impurities along the boundaries [10,11]
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