Atomic Structures of Planar Defects in Si and GaAs
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ATOMIC STRUCTURES OF PLANAR DEFECTS IN Si AND GaAs
S. TAKEDA, S. MUTO AND M. HIRATA Department of Physics, College of General Education, Osaka University, Toyonaka, Osaka 560
ABSTRACT Atomic structures of planar defects in Si and GaAs have been studied by TEM. An HREM image of the edge of 11131 planar defect has been obtained with incidence. An analysis of the image has showed that the edge consists of 5-, 6- and 7-membered rings without dangling bond. Anisotropic morphology of the defect could be understood from the model proposed in this report. Weak diffuse scattering and an extinction rule in diffraction patterns from the defect have been found. The experimental evidence has supported the model of the 1113) defect. A planar defect on (111 ) in a heavily Si doped GaAs has been studied. The result has indicated that Si precipitates on the two [ 111 net planes inserted in the GaAs matrix.
INTRODUCTION Various different processes to fabricate devices induce defects on the common crystallographic planes such as {111 ) and [ 1131. These planar defects are easily detected in TEM, and the nature of them can be determined by TEM technique. However, atomic arrangement in some planar defects has remained uncertain, and this fact may induce unnecessary confusion in the understanding of the formation process of such defects . Even though solving atomic structures of defects may not be current issues in device fabrication, it offers reliable basic data toward more quantitative study of defect engineering. Some planar defects in Si and GaAs have been studied by diffraction and imaging technique in TEM as well as EDX. The structural models reveal new kinds of lattice-reconstruction in the interior of a crystal involving interstitials and impurities in semiconductors. TEM SPECIMENS FOR STRUCTURAL STUDIES OF PLANAR DEFECTS Structural data of planar defects were obtained by transmission electron diffraction (TED) and high resolution electron microscopy (HREM). TED patterns were recorded with several incidence directions including plan-view incidence, while HREM images were taken in crosssectional geometry. Planar defects which were induced by electron irradiation or ion-implantation were usually located inside of a crystal, and hence, in order to observe a clear TED pattern of the defect, TEM specimens were prepared as follows. 1) The wafer whose surface was nearly parallel to the defect plane was used. 2) After both surfaces of a disc of 3mm in diameter were dimpled, chemical etching was performed until the discs were perforated. 3) Defects were introduced by electron irradiation or ion implantation followed by heat treatment. 4) Both surfaces of the discs were etched by Ar ion (4kV) in order to remove perfect crystals near the top and bottom surfaces until a clear TED pattern from the defect was observed. Since the planar defects were not always located in the middle part of a thin foil specimen, etching time for a surface was usually different from that for the other surface. For cross-sectional HREM observation in the inci
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