Point-defect properties in ion-irradiated Si were investigated using in situ grazing incidence diffuse x-ray scattering. Bombardment with 4.5-keV He at 100 K and 3-MeV electrons at 6 K led to the production of Frenkel pairs. These defects are characterized by close-pair configurations and by relaxation volumes of vacancies and interstitials that have nearly the same magnitude, but opposite sign. Thermally activated motion of interstitial atoms occurs above Ϸ150 K, while that for vacancies occurs above Ϸ175 K. The motion of interstitials below 150 K during electron irradiation is shown to be induced by electronic excitation, and it is negligible for ion irradiations. Similar results were observed for irradiation with 20-keV Ga and 1.0-MeV Ar, although the defects were already clustered upon bombardment at 100 K. Correlation distances between vacancies and interstitials in cascades are obtained.
Diffuse x-ray scattering is a powerful means to study the structure of defects in crystalline solids. The traditional analysis of diffuse x-ray scattering experiments relies on analytical and numerical methods which are not well suited for studying complicated defect configurations. We present here an atomistic simulation method by which the diffuse x-ray scattering can be calculated for an arbitrary finite-sized defect in any material where reliable interatomic force models exist. We present results of the method for point defects, defect clusters and dislocations in semiconductors and metals, and show that surface effects on diffuse scattering, which might be important for the investigation of shallow implantation damage, will be negligible in most practical cases. We also compare the results with x-ray experiments on defects in semiconductors to demonstrate how the method can be used to understand complex damage configurations.
Radiation-induced damage and strain in AlAs were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar, and Au ion beams at 25 or 80 K. The out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. Selected samples were examined by high-resolution and conventional transmission electron microscopy. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.
X-ray diffraction and channeling-Rutherford backscattering spectrometry (RBS) were employed to investigate damage accumulation in AlxGa1−xAs (x=0.50, 0.75, 0.85, and 1.0) irradiated at 80 K with MeV ions. The x-ray measurements, performed both before and after warming the samples, showed a transition in the strain accumulation behavior as the Al content increased. For samples with low Al content, x=0.50, the strain increased monotonically with fluence until the sample amorphized, a behavior similar to GaAs. For samples with x⩾0.75, the strain initially increased, then plateaued, and finally diminished at high fluences. The RBS data, obtained at both 80 K and room temperature, revealed a similar dependence of the amorphization behavior upon Al content. For pure AlAs films, amorphization in the bulk was not observed even after a fluence of 2×1017 cm2 of 1.7 MeV Ar+. For films with low Al content, however, the AlxGa1−xAs layer readily amorphized with a fluence of only 6.8×1014 cm2 of 1.7 MeV Ar+. From these data, along with previously published information provided by transmission electron microscopy studies, a model for damage accumulation in ion irradiated AlxGa1−xAs is proposed.
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