TEM STUDY OF NIGA/(001)GAAS AND GAAS/NIGA/(001)GAAS HETEROSTRUCTURES

Intermetallic NiGa epitaxial layers were deposited by molecular beam epitaxy, on (001) GaAs substrates at 120-degrees-C. The TEM results point out the difficulty in avoiding the nucleation of hexagonal phase(s) (either Ni or Ga rich) together with the NiGa phase. Only the use of a precursor Ni rich surface allows the stabilization of a monocrystalline cubic NiGa layer at the interface, up to a thickness of about 12 nm; in these conditions, heterostructures with thin (3 to 12 nm) buried good quality NiGa layers were grown. The lower interface is flat at the atomic scale, but the roughness of the upper layer interface leads to a high density of defects in the GaAs overlayer.