Surface dislocations were revealed in single crystal CdZnTe and CdTe samples using chemical etching.
Dislocation etch pits on the Te dominant (111)B face were studied under optical, infrared and scanning electron
microscopes. The samples came from crystal ingots which were grown using different chemical compositions and
applied growth parameters. From these ingots, etch pit density, shape and distribution were examined and compared with
the varying growth techniques. Resistivity and mobility-lifetime product, μτe, properties of the detectors were measured.
A combination of detector grade and non-detector grade ingots were tested. Near infra-red microscopy was used to
compare the amount of secondary phases present in the bulk of the crystals with dislocation etch pits on their surface.
Semiconducting CdZnTe or "CZT" crystals are very suitable for use as a room temperature-based gamma
radiation spectrometer. During the last decade, modifications in growth methods for CZT have significantly improved
the quality of the produced crystals however there are material features that can influence the performance of these
materials as radiation detectors. For example, various structural heterogeneities within the CZT crystals, such as, pipes,
voids, polycrystallinity, and secondary phases (SP) can have a negative impact on the detector performance. In this
study, a CZT material was grown by the modified vertical Bridgman growth (MVB) method with zone leveled growth
in the absence of excess Te in the melt. Numerous SP were imaged using transmission IR at a volume % of 0.002.
Samples from this material were analyzed using various analytical techniques to evaluate its electrical properties, purity
and detector performance as radiation spectrometers and to determine the morphology, dimension and elemental
/structural composition of one of the SP in this material. This material was found to have a high resistivity and good
radiation spectrometer performance. It had SPs that were rich in calcium (Ca), carbon (C) and oxygen (O) (possibly
CaCO3) or only C and O that were 5 μm or less in diameter.
CdZnTe or "CZT" crystals are highly suitable for use as a room temperature based spectrometer for the
detection and characterization of gamma radiation. Over the last decade, the methods for growing high quality CZT
have improved the quality of the produced crystals however there are material features that can influence the
performance of these materials as radiation detectors. For example, various structural heterogeneities within the CZT
crystals, such as twinning, pipes, grain boundaries (polycrystallinity), and secondary phases (SP) can have a negative
impact on the detector performance. In this study, a CZT material was grown by the modified vertical Bridgman
growth (MVB) method with zone leveled growth without excess Te in the melt. Visual observations of material from
the growth of this material revealed significant voids and SP. Samples from this material were analyzed using various
analytical techniques to evaluate its electrical properties, purity and detector performance as radiation spectrometers and
to determine the morphology, dimension and elemental /structural composition of one of the SP in this material. This
material was found to have a high resistivity but poor radiation spectrometer performance. It had SP that were rich in
polycrystalline aluminum oxide (Al2O3), metallic Te and polycrystalline CdZnTe and 15 to 50 μm in diameter. Bulk
elemental analyses of sister material from elsewhere in the boule did not contain high levels of Al so there is
considerable elemental impurity heterogeneity within the boule from this growth.
Low pressure Electro-Dynamic Gradient freeze (EDG) method has been used to
grow compensated, high resistivity Cd(1-x)ZnxTe for x and gamma ray detectors. All
growths contained excess Tellurium which is added to the growth. Ampoule design and
setup to limit vapor transport was determined to be important. Ingots grown in a Pyrolitic
Coated Graphite crucible are shown to provide a good response to ionizing radiation at
room temperature and can be used multiple times. The highest doping levels of
Aluminum are shown to improve mobility lifetime products for electrons and average
8.7x10-4 cm2/V at 0.5 μsecond shaping fitting the Hecht relation.
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