Study of Te nanoprecipitates in CdZnTe crystals
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Shao-Ju Shih Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
Shichun Mu State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
Yadong Xu and Wanqi Jie State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China (Received 24 June 2009; accepted 22 September 2009)
In-depth studies of the two types of Te nanoprecipitates, linear and elliptic, in Cd1–xZnxTe (CZT) crystals grown by a modified vertical Bridgman method have been carried out. Electron diffraction suggests that linear Te nanoprecipitates align their Te atoms in a similar way to CZT structure, while elliptic Te nanoprecipitates cluster Te atoms following the pure trigonal Te structure. The three-dimensional morphology for both linear and elliptic Te nanoprecipitates has been revealed by delicate energy-dispersive x-ray analysis under electron microscopy. The density of elliptic Te nanoprecipitates ranges from 1015 to 1017 cm3, while linear ones usually several times lower for a certain CZT wafer. The origin of both types of Te nanoprecipitates has been discussed in terms of the local density of intrinsic point defects in CZT. CZT properties are influenced more negatively by elliptic Te nanoprecipitates, which shed light on the methodology for crystal growth: preventing the clustering of intrinsic point defects during the crystal growth will be essential to obtain high quality CZT crystal.
I. INTRODUCTION
The II-VI compound semiconductor Cd1–xZnxTe (CZT) possesses the following characteristics including: (i) high atomic number; (ii) high room-temperature band gap energy; (iii) good mechanical strength; (iv) high resistivity; (v) higher photosensitivity; and (vi) relatively good charge transport properties,1–6 which make CZT a superior candidate for various industrial applications, such as farinfrared (IR) and radiation detectors,1–4 solar cells,5 photorefractive devices,6 biomedical devices,7,8 etc. However, suffering from its low defects formation energy, CZT is vulnerable to a variety of structural defects, such as Cd vacancies, Te interstitials, Te antisites, dislocations, twins, Te-rich phases, etc.9–12 These defects spoil CZT optoelectronic properties and hence the performance of CZT devices. For this reason, enormous effort has been placed on the study of CZT defects in the past decades. To understand the formation mechanism and to reduce the density of defects, knowledge of defect structures is a)
Address all correspondence to this author. e-mails: [email protected]; [email protected] DOI: 10.1557/JMR.2010.0171 1298
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 7, Jul 2010 Downloaded: 13 Mar 2015
very important. Cd vacancies and Te interstitial and antisites are difficult to observe by experimental approaches; therefore, they are usually investigated by theoretical calculation.13 Dislocations and twins can be directly watched under scanning electron micr
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