Core-level photoemission study of MBE-grown GaAs(111) and (100) surfaces

MBE-grown GaAs(111) and (100) surfaces have been investigated using synchrotron radiation photoemission spectroscopy. A least-squares fit routine has been used to decompose the various contributions to the core-level line shape. For the As-terminated GaAs(111) surface, the As(3d) and Ga(3d) line shapes and intensities show that the surface coverage of As exceeds one monolayer and that only surface As atoms are involved in the reconstruction. Further, they indicate that the vacancy model developed for the Ga-terminated GaAs(111) surface cannot be extended to the As-terminated GaAs(111) surface. Distinct differences have been observed between primitive [4×6] and centered [c(4×4) and c(2×8)] GaAs(100) reconstructions. For the GaAs(100)c(4×4) surface, our results provide a better resolution of structure associated with 1/4 of a monolayer of an amorphous As overlayer from features arising from the order reconstructed layer. Our results suggest that the transfer of charge between Ga and As atoms occurs during the transformation of c(4×4) into c(2×8). Further, they show that the relative energy positions of the deconvoluted peaks are more characteristic of the different surface reconstructions. The heterojunction interface formation between As-terminated GaAs(111) and three surface reconstructions of GaAs(100) and Ge was studied. The observed differences among the various GaAs starting surfaces do not affect the band offset by more than the experimental uncertainty of ±0.05 eV.