Application of Channeling to Defect Studies in Crystals
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APPLICATION OF CHANNELING TO DEFECT STUDIES IN CRYSTALS
W. K. Chu IBM General Technology Division, East Fishkill, Hopewell Junction, New York 12533 ABSTRACT Channeling of fast, light ions in crystals has been Backwidely used as a tool for studying crystal defects. scattering yield measurement on ions incident along major axial or planar crystalline directions provides information on the depth distribution of the structural defects in the first few microns. The channeling technique in defect detection is not as sensitive as Transmission Electron Spectroscopy, nor is it accurate in measuring the absolute numbers of defect density. Channeling measurements can give It is only an indication of the degree of lattice disorder. possible to distinguish one type of defect from another by carefully studying the energy dependence of the dechanneling. The dechanneling interpretation is not always unique, and in practice it is difficult to obtain structure information through that method. Despite these negative qualities, channeling is an attractive and unique method in certain For example, it is sensitive for studying defect studies. the lattice location of impurity atoms at substitutional or sites. Clustering of substitutional impurity interstitial atoms will show a displacement of the impurity atoms from lattice sites due to the change of bond distance. Channeling is sensitive for measuring impurity displacement as small as 0.1A. This has been demonstrated in the study of arsenic Interfacial relaxation and clustering formation in Si. contraction in a multi-layered structure made by molecular beam epitaxy has been detected by dechanneling along various Channeling study on surface and interface axial directions. In this structures has developed over the past few years. paper, I will use examples to illustrate the unique features of the channeling technique and its application to defect studies in single crystals.
INTRODUCTION discussed and predicted in 1912 by Stark(1) Channeling phenomenon was first His paper on the subject was ignored and forgotten, however, perhaps due to a lack of instrumentation and the birth of atomic and nuclear physics. Half a
(2)
during a century later, the phenomenon was rediscovered by Robinson and Oen computer simulation on the directional dependence of the penetration depth of Experimental evidence for channeling charged particle in single-crystal solids. was obtained almost simultaneously in different labs during 1963. In 1965 Lindhard(3) gave a theoretical description of channeling phenomenon. HE said that charged particles penetrating the single crystal along or near a major axis are experiencing a collective string potential produced by the rows of atoms along that axis. If the incident direction of the ion beam
118 is nearly parallel with the string of atoms, the string potential will steer the charge particle beam forward. A critical angle is defined as the limiting angle between the incident direction and row of atoms such that the steering effect exists. When charged particles ar
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