Defect structure and electrophysical parameters of GaAs implanted with C+, Ne+, Ar+, C+ +Ne+, and C+ + Ar+ ions are studied by means of electron microscopy and Hall measurements. The results are explained in terms of the hypothesis according to which an increase in the irradiation dose results in a change of the dominating process which causes nonstoichiometry in subsurface regions. At doses below the threshold dose such regions are enriched with As. at those above it with Ga.
As a first Born approximation to the two‐wave dynamical theory of electron diffusion, changes in the phases of transmitted and diffracted waves on the exit surface of a crystal containing small defects are considered. The relationship between the phase distribution, the foil thickness, and the defect location depth is analysed. It is shown that phase information is helpful in identifying the type of imperfection (interstitial or vacancy) in cases when focused images have no black‐and‐white contrast.
Theoretical electron micrographs are constructed for edge dislocations located parallel to the foil surface and normally to the electron beam at g · b = 0 and s = 0. It is shown that these images are essentially different for two versions of taking into account the stress relaxation on the foil surface: a) by introducing a single image dislocation, b) by introducing, along with the image dislocation, an additional stress source, compensating a “fictitious” tangential component of the stress field. The empirical method of determining the nature of dislocation loops by the analysis of residual contrast at g · b = 0 and s = 0 is supported by the theoretical images.
A computer calculation of the redistribution of the displacement field gradient which is due to the surface stress relaxation is made for a crystal with an edge dislocation parallel to the foil surface and gliding in the plane normal to the surface. The theoretical analysis of the specific features of the electron‐microscopy images, associated with the stress relaxation on the free surfaces, is based on the obtained regularities of the displacement distribution. Relaxation leads to a change of the background level about which the dislocation images are oscillating when the location depth of defects is varied. It is shown that relaxation effects are different in the bright‐field and dark‐field micrographs.
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