STUDY OF SOLID-STATE INTERDIFFUSIONS IN T HE NI ALAS CONTACT/

Solid-state interdiffusions between a thin film of nickel deposited un der vacuum conditions and a thick layer of epitaxial AlAs on GaAs (001 ) and (111) substrates were investigated in the temperature range 200- 600 degrees C. Complementary analytical methods (RES, X-ray diffractio n, TEM) allow us to point out, according to annealing temperatures, su ccessives steps of the interaction. These steps correspond either to t ernary phases which were evidenced by the experimental determination o f the Ni-Al-As phase diagram and labelled as A, B and D phases by comp arison with the isostructural ternary phases in the Ni-Ga-As diagram o r to mixture of ternaries and binaries, more or less strongly textured on the substrate. In fact, the nature of the observed phases is stron gly depending on the AlAs substrate orientation, the kinetic of the re action occurring being slower on AlAs(111) than on AlAs(001). On AlAs( 001), a ternary B-phase + NiAl mixture is firstly observed, followed b y a second mixture constituted of the ternary A-phase + NiAl and NiAs binaries, and finally, at the end of the interaction, the two binaries NiAl + NiAs appear. On AlAs(111), only two steps of interaction have been found; first of all, the ternary D-phase is obtained, before lead ing, at the end of the interaction, to the ternary B-phase + NiAl + Ni As mixture. In that case, the 600 degrees C annealing is not sufficien t to reach the mixture of the binaries NiAl + NiAs which, according to the ternary phase diagram, is the final stage of the Ni/AlAs interact ion. The comparative study of the Ni/AlAs and Ni/GaAs interdiffusions shows that the binary NiAl is the ''key'' compound around which the Ni /AlAs interaction progresses when NiAs is the one of the Ni/GaAs inter action. The binary NiAl which is thermally stable and strongly texture d on AlAs appears as an interesting candidate to prepare epitaxial NiA l/AlAs/GaAs heterostructures.