Rare earth metal/semiconductor interfaces and compounds

Interfaces formed at room temperature by incremental deposition of rare earth metals onto semiconductor substrates were studied with surface sensitive soft x-ray photoelectron spectroscopy. The trends in core level lineshape and intensity with increasing metal coverage were used to deduce an outline of the evolution and the final morphology of the interfacial region on a microscopic scale. Measurements were taken for Yb on Si, He, and GaAs, and for Gd and Eu on Si. The Yb/Si interface work was supported by comparable measurements of bulk Yb silicide samples of known composition and crystal structure. In a general sense, the behavior of all the systems studied is similar. At very low metal coverages, the metal atoms chemisorb and are weakly bonded to the substrate. The 4f core levels indicate that the metal-metal atom coordination is relatively low at this stage. The interaction with the substrate strengthens with increasing coverage, culminating in the formation of a strongly reacted phase at between 1 and 3 monolayers (ML). The strong reaction is limited to a narrow region at room temperature. At less than 10 ML coverage, the surface of the sample is almost indistinguishable from the pure metal. Details of the behavior such as the reactivity at low coverage, the compounds formed at the interface, the morphology at the surface at intermediate coverages, the final interfacial width, and the amount of substrate atom outdiffusion and surface segregation can all vary from system to system