Strong chemical reactivity at the early stages of Yb overgrowth on GaP(110): A synchrotron-radiation study

The GaP(110)/Yb interface was studied with use of synchrotron radiation to excite the Ga 3d and the P 2p semiconductor core levels, the quasiatomic Yb 4f states together with the valence-band region, and the P L2,3VV Auger line shape in Yb coverages ranging from 0.2 to 5 monolayers. Strong reactivity was found at the interface region with semiconductor surface disruption and the formation of intermixed Yb-Ga-P products distributed on the substrate surface from the lowest coverage range investigated up to about 1 monolayer. Ga surface segregation with Yb-Ga alloying and Yb phosphide-like product trapping at the interface are dominant in the highest coverage range, resulting in a strong gradient concentration of the substrate chemical species, along a direction normal to the semiconductor surface. The reacted contributions in the Ga 3d, the P 2p, and the Yb 4f levels suggest a highly heterogeneous character of the growing interface with the presence of a multiplicity of atomic sites for each of the reacted atoms. Primarily divalent character of Yb atoms was found over all the coverage range investigated, as derived by Yb 4f spectroscopy. From the changes shown by the P L2,3VV line shape it was possible to model the evolution of the local density of states in Yb-P bonds in terms of Yb 5d- and P 3p-derived states mixing. The results are compared with the growth mechanisms of other III-V-semiconductorrare-earth-metal interfaces.