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Epitaxial growth of rare-earth trifluorides on III-V semiconductors Ritchie, Sayuri


Epitaxial growths of rare-earth trifluorides on III-V semiconductors have been investigated. Synchrotron photoemission spectroscopy showed a complete coverage of III-V substrates by LaF₃ and ErF₃ films and interfacial chemical reactions at the interface. In the LaF₃ films on GaAs(lll) substrates, residual tensile strains were detected by highresolution X-ray diffraction (HRXRD) contrary to the expected compressive strains in the case of a pseudomorphic growth. The tensile strains are interpreted as being due to the differential thermal contractions of the fluorides and the semiconductors during cooling. The correlations between the bulk structure and the surface structure of the LaF₃ films on GaAs and InP substrates have been studied by X-ray rocking curve measurements, grazing incidence X-ray scattering and atomic force microscopy. The lateral coherence lengths in the LaF₃ films from the X-ray rocking curves and the height-height surface correlation lengths from the X-ray scattering and the atomic force microscopy were comparable to each other and were associated with the lattice mismatch of the system at the growth temperature. The results are interpreted in terms of strain relieving defects surrounding the columns of coherent crystals. The kinetics of LaF₃ film growths on III-V semiconductors were investigated using the self-affine surface structure analysis for the X-ray specular/diffuse scattering and the atomic force microscopy. The scaling exponents for the film growth obtained from the analysis were closest to the exponents predicted by the Villain-Lai-Das Sarma model in which the surface diffusion of deposited particles is the most important process in the film growth. InP single crystal islands have been grown on LaF₃/InP(lll) heterostructures. The InP islands are observed to be faceted with three-fold symmetry as expected for (111) orientation. A small broadening of the InP substrate diffraction peak is interpreted as being due to inhomogeneous strains associated with the InP islands and differential thermal contraction of the LaF₃ films during cooling.

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