2-DIMENSIONAL ELECTRONIC-STRUCTURE EI(KI-PARALLEL-TO,KI-PERPENDICULAR-TO) OF GAAS(001) STUDIED BY ANGLE-RESOLVED PHOTOEMISSION

Angle-resolved photoemission techniques have been used to study the occupied band structure of the As-terminated GaAs(001)-1 X 1 surface grown by molecular-beam epitaxy. The measurements were taken along the [100] azimuth and covered the photon-energy range 10-70 eV. Structure plots involving linear-muffin-tin-orbital (LMTO) calculated valence bands and free-electron-like final states (FELFS's) were used to interpret the acquired data, which included normal-emission spectra at various photon energies and off-normal-emission spectra at selected photon energies. A structure plot of initial energy (E(i)) versus polar-emission angle (theta) was employed to interpret the two-dimensional electronic structure E(i)(k(i)parallel-to, k(i)perpendicular-to) observed from off-normal-emission spectra, where k(i)parallel-to and k(i)perpendicular-to are, respectively, the parallel and perpendicular components of the wave vector of the valence electrons to the sample surface. It was found that the majority of strong transitions could be explained as direct transitions from LMTO valence bands to primary or secondary cones of FELFS's. The FELFS model was found to have mixed success over the entire photon-energy range investigated. We show, in particular, that the assignment of transitions can be misleading if only normal-emission spectra are considered.