Depth Sensitive Imaging of Defects in Epilayers and Single Crystals Using White Beam Synchrotron Radiation Topography in
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DEPTH SENSITIVE IMAGING OF DEFECTS IN EPILAYERS AND SINGLE CRYSTALS USING WHITE BEAM SYNCHROTRON RADIATION TOPOGRAPHY IN GRAZING BRAGG-LAUE GEOMETRY. M. DUDLEY,' G.-D. YAO,5 J. WU,- AND H.-Y. LIU," * Dept. of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook NY 11794. ** Materials Science Laboratory, Texas Instruments Inc., P.O. Box 655936, Mail Stop 147, Dallas, TX 75265.
ABSTRACT. The technique of Synchrotron White Beam topographic imaging in grazing BraggLaue geometries has been developed at the Stony Brook synchrotron topography station at the NSLS. This technique enables imaging of defects in subsurface regions of thickness which can range from hundreds of Angstroms to hundreds of microns as determined by the penetration depth of the X-rays. This penetration depth, which is shown to be determined by the kinematical theory of X-ray diffraction, can be conveniently varied, in a controlled manner, by simple manipulation of the diffraction geometry, thereby enabling a depth profiling of the defect content. The fundamentals of the technique are described, and its advantages and disadvantages compared to existing techniques are discussed in detail. Examples of application of the technique in the characterization of defects in thin epitaxial films of GaAs on Si, are given, and the general applicability of the technique is discussed.
INTRODUCTION. The characterization of the defect content in thin subsurface layers of single crystals has importance in many branches of Materials Science, ranging from technologically important areas such as characterization of semiconductor and superconductor heterostructures, respectively, to areas of more esoteric but nonetheless fundamental importance such as characterization of organic single crystals undergoing UV induced solid state reactions (which are often near surface reactions). This paper addresses primarily the former of these applications. Examples of applications in the other areas will be published in separate papers. Among the techniques capable of imaging and characterizing the defect and strain content in thin subsurface layers, X-ray topographic imaging is the most strain sensitive, with a capability of detecting strains (Ad/d) in the range of 10- and smaller. Transmission X-ray topography and reflection X-ray topography in the Conventional-Bragg geometry have been routinely used to characterize the defect content in bulk semriconductor crystals for many years. However, when it comes to characterizing thin epitaxial films, the transmission technique has very limited depth sensitivity (based on subtle contrast variations), and even the conventional-Bragg geometry reflection technique has. limitations in determining the position of a defect with respect to the crystal surface. In these latter geometries, (e.g. the Berg-Barrett technique), as in all reflection type geoinetries, it is well known that information can only be obtained from the volume defined by the effective area of the incident beam on the crystal surface and the
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