PHOTOEMISSION-STUDY OF GD METAL OVERLAYERS ON A GAAS(110) SURFACE

We have studied the chemical reactions of Gd metal on an in situ cleav ed GaAs(110) surface by photoemission spectroscopy of Ga 3d and As 3d core-levels as well as the Gd 4f level on- and off-resonance valence b and using synchrotron radiation. We find that the Fermi-level pinning is completed before 0.13 ML coverage, and the deposited Gd atoms start to react with the GaAs substrate at a very low coverage (critical cov erage < 0.067 ML). As more Gd atoms are deposited, they form stable co mpounds with As atoms which are then trapped in the relatively narrow interfacial layer of thickness less than about 3.3 ML, while Ga atoms diffuse out towards the surface and eventually become metallic. The th ickness of the Gd-Ga intermixed layers is estimated to be about 6.7 ML , which is somewhat greater than that for a Gd/Si(lll) interface.