VACUUM STABILITY OF EPITAXIAL NIGA AND NI2GA3 LAYERS MBE GROWN ONTO A GAAS SUBSTRATE

Metallic epilayers of NiGa (cubic) and Ni2Ga3 (hexagonal pseudo-cubic) were grown onto a GaAs substrate in a molecular beam epitaxy system. With the intent to grow a semiconductor/metal/semiconductor structure, the stability of the NiGa/GaAs and Ni2Ga3/GaAs systems, at 500°C in ultra-high vacuum, under an As4 flux, was studied by transmission electron microscopy. The behaviour of the two compounds appears to be different: NiGa interacts with GaAs, and due to As sublimation, this interaction leads to Ni2Ga3; on the other hand, Ni2Ga3 is thermodynamically stable in contact with GaAs. However, the Ni2Ga3 epilayer tends to agglomerate, onto a (001) GaAs substrate as well as a (111) one, and the stability of the film is not preserved at 500°C. Moreover, onto a (001) substrate, the Ni2Ga3 layer is observed to be composed of twinned domains, because of the symmetry difference between the two phases in the interface plane. Anyway it is concluded that the growth of a GaAs overlayer onto NiGa and Ni2Ga3 films will have to be performed at low temperature. © 1990.