X-ray Topography to Characterize Surface Damage on CdZnTe Crystals
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1038-O04-03
X-ray Topography to Characterize Surface Damage on CdZnTe Crystals David Black1, Joseph Woicik1, Martine C. Duff2, Douglas B. Hunter2, Arnold Burger3, and Michael Groza3 1 NIST, Gaithersburg, MD, 20899 2 SRNL, Aiken, SC, 29808 3 Fisk University, Nashville, TN, 37208 ABSTRACT Synthetic CdZnTe or “CZT” crystals can be used for room temperature detection of αand γ-radiation. Structural/morphological heterogeneities within CZT, such as twinning, secondary phases (often referred to as inclusions or precipitates), and polycrystallinity can affect detector performance. As part of a broader study using synchrotron radiation techniques to correlate detector performance to microstructure, x-ray topography (XRT) has been used to characterize CZT crystals. We have found that CZT crystals almost always have a variety of residual surface damage, which interferes with our ability to observe the underlying microstructure –for purposes of crystal quality evaluation. Specific structures are identifiable as resulting from fabrication processes and from handling and shipping of sample crystals. Etching was found to remove this damage; however, our studies have shown that the radiation detector performance of the etched surfaces was inferior to the as-polished surface due to higher surface currents which result in more peak tailing and less energy resolution. We have not fully investigated the effects of the various types of inducible damage on radiation detector performance. INTRODUCTION Synthetic CdZnTe (CZT) crystals can be used for room temperature detection of gamma radiation. However, the radiation detection properties of CZT crystals vary widely. These variances are not well understood but they have been attributed to structural and morphological heterogeneities within the crystals, such as twinning, secondary phases and polycrystallinity [15]. Such heterogeneities often result in poor γ-ray detection performance. To improve our understanding of the relationship between microstructure and detector performance we have developed a broad program to utilize a variety of characterization techniques to investigate the microstructure of CZT crystals and correlate it to detector performance. We report the results of our examination of CZT crystals using synchrotron based x-ray diffraction topographic imaging. The microstructure of a crystal reveals information about the quality of the crystal. Crystal quality is often attributed to low overall crystal strain, the absence of twins and grain boundaries, and in many cases, the absence of secondary phases [6 and references therein]. Crystal attributes such as these are often good indicators of detector performance [6 and references therein]. These types of features can often be observed by topography and x-ray topography can be used to investigate the crystal quality that is beyond the surface. However, surface damage can obscure the view of the deeper features within crystals that can reveal crystal quality. This paper focuses on the various factors that contribute to surface d
