Sippel, P.; Supplie, O.; May, M.M.; Eichberger, R.; Hannappel, T.: Electronic structures of GaP(100) surface reconstructions probed with two-photon photoemission spectroscopy. Physical Review B 89 (2014), p. 165312/1-8
10.1103/PhysRevB.89.165312

Abstract:
The electronic structures of two significant atomically well-defined (100)-surface reconstructions of gallium phosphide were investigated with two-photon-photoemission spectroscopy (2PPE). We allocated a series of occupied and unoccupied surface states and deduced the influence of each particular reconstruction on the electronic structure of the surface. Photoemission signals arising from bulk optical transitions were distinguished from surface-state related signals by studying the influence of oxygen exposure to the surfaces and by comparing our results to reflectance anisotropy spectroscopy (RAS) measurements. This revealed that the features in the RAS signal correlate with the transition energies between unoccupied and occupied surface-related states that were observed in the 2PPE measurements. An anisotropy around the E0′ critical point, previously known from RA spectra, was also investigated with 2PPE and is ascribed to modifications of the bulk electronic structure in the vicinity of the surface.