EPITAXIAL-GROWTH, STRUCTURE, AND COMPOSITION OF FE FILMS ON GAAS(001)-2X4

The structure and composition of Fe films grown on As-terminated GaAs( 001)-2x4 surfaces at 175 degrees C has been studied in situ with scann ing tunneling microscopy (STM), photoelectron diffraction (FED), and x -ray photoelectron spectroscopy (XPS). The GaAs surfaces were prepared by molecular beam epitaxy (MBE) and exhibited large atomically well-o rdered terraces. We find that the 2x4 reconstruction has a significant impact on the Fe nucleation and growth, with initial nucleation occur ring at As-dimer sites. STM reveals that the first half-monolayer of F e forms small two-dimensional islands along the As-dimer rows before g rowing onto the adjacent Ga-rich rows, with no evidence of substrate d isruption. FED indicates that the growth is predominantly layer by lay er, with the growth front for the nth deposited layer limited to the ( n+1)th layer. XPS spectra show that the Fe films include a concentrati on gradient of Ga and As out-diffused from the interface, with some of the As segregating to the Fe surface, similar to previous results obt ained for growth on non-MBE prepared GaAs surfaces. Possible mechanism s for the film growth and the origins of the intermixing are discussed . (C) 1996 American Vacuum Society.