Characterization of Infrared Materials by X-Ray Diffraction Techniques
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CHARACTERIZATION OF INFRARED MATERIALS BY X-RAY DIFFRACTION TECHNIQUES W. J. TAKEI and N. J. DOYLE, Westinghouse R&D Center, 1310 Beulah Road, Pittsburgh, PA 15235 ABSTRACT X-ray diffraction techniques have proved invaluable in the characterization of infrared materials, particularly those prepared by thin The film deposition techniques such as molecular beam epitaxy, MBE. techniques are sufficiently sensitive and rapid to provide the information feedback required for efficient optimization of the growth process. They are nondestructive and permit the correlation with results on the same sample obtained by other characterization techniques such as those being described at this Symposium. Depending on the development status of the growth technology, the information to be acquired includes presence of twinning, quality, and type of epitaxial orientation, strains, and compositional variations. A critical issue in the application of these materials in detector arrays is the question of uniformity control, both laterally and in depth. The techniques to be described include not only modern x-ray topographic and multiple crystal diffractometric techniques but particularly for the early stages of growth process development, classical photographic ones such as the oscillation and Weissenberg methods. Examples of these various aspects are presented with emphasis placed on the characterization involved in MBE growth of HgCdTe films.
INTRODUCTION A viable IR materials and device technology depends critically on characterization of the materials. Process optimization can be achieved only
with a knowledge of the effect of parameters on the structure and properties of the materials which result. These factors are equally important in developing the high performance IR detectors which are the ultimate goal of this effort. This is particularly true in the case of BgCdTe with its difficulty in control of composition, crystallographic quality, and electrical
properties.
The promise of improved quality and practical requirements of
device configurations have led to a focus on epitaxial growth methods, LPE, MOCVD, and MBE. This in turn has led to the need to study, not only active
layers and interfaces, but also the substrate which provides the foundation for the entire process.
A wide variety of techniques, many described in other papers at this Symposium, have been used to understand the material and process under study.
The integration of the techniques in the development of our MBE program has been described previously [1-3]. In this paper one important class of techniques will be reviewed -- those utilizing x-ray diffraction. The approach adopted is a practical one, illustrating the type of information achievable by example for various techniques. The intent is not to provide a detailed understanding of various x-ray techniques but to give a general survey of their utility in the study of IR materials. More details are given in various surveys.[4-6]
GENERAL CONSIDERATIONS The importance of x-ray diffraction characterizati
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