STUDY OF SOLID-STATE INTERDIFFUSIONS IN T HE ER GAAS CONTACT

Solid state interdiffusions between a thin film of erbium deposited un der vacuum conditions and (001) and (111) GaAs substrates were investi gated in the temperature range 350-800-degrees-C. Complementary analys is methods (RBS, X-ray diffraction) allow us to point out, according t o annealing temperatures, successives steps of the interaction corresp onding to different mixtures of phases, essentially binaries. These st eps are strongly depending on the GaAs substrate orientation, especial ly the final step of the interdiffusions. On (001) GaAs, only two step s have been observed : no visible interaction is noticed between erbiu m and GaAs before 600-degrees-C; the interaction begins at 600-degrees -C. evolves slightly and leads at 800-degrees-C to the nominal composi tion << Er10GaAs >> which corresponds to a mixture of several phases E r5Ga3, Er and ErAs. On (111) GaAs. several steps of interaction have b een found ; first of all, erbium reacts with the substrate at 400-degr ees-C (Er5Ga, + Er mixture). then the reaction is continuing at 600-de grees-C (Er5Ga3 + Er + ErAs mixture) before reaching at 800-degrees-C the nominal composition << Er1.5GaAs >>, which is in fact a mixture of the three binaries ErAs + ErGa2 + Er3Ga5. It can be noticed that the 800-degrees-C annealing is not sufficient to reach the mixture of the phases ErAs + Ga which, according to the ternary phase diagram, should be the final stage of the interaction Er/GaAs. The analysis of the Er /GaAs interdiffusions shows that ErAs is the << key >> compound around which the interaction progresses. This compound appears as an ideal c andidate to realize epitaxial ErAs/GaAs heterostructures.