Comparative Studies of Electron Affinities and Work Functions for GaAs and Si

摘要

Ultra-violet Photoemission Spectra (UPS) involving core level photoemission peaks (Ga 3d for GaAs and Si 2p for Si) is measured for the (111), (110), (111), and (001) surfaces of GaAs and Si using the light from a Helium lamp (21.2 eV and 40.8 eV) and from the Berlin synchrotron radiation source BESSY (108.6 eV), respectively. These surfaces are prepared by ion bombardment and annealing on cylindrically shaped GaAS and Si crystals with 110 as their axis. The GaAs cylinder is in addition prepared by molecular beam epitaxy yielding As-rich phases on (111) and (001). The work function Phi and the electron affinity x are evaluated from the low energy (secondary electron) threshold and the energy position of the core level photoemission peak. It is shown that due to the crystal polarity and differences in surface composition, the electron affinity depends strongly on the orientation for GaAs. For Si, the missing bulk polarity is responsible for the small variations of X, which may be caused by the different surface reconstructions. On GaAs, the Variation of Phi and X are essentially parallel indicating no strong band bending variations. On Si, however, the relatively strong variations of Phi indicate strong variations of the band bending.