The effects of crystal defects near the surface on the position of surface Fermi level (Es) are investigated using photoluminescence (PL) measurements and synchrotron radiation photoelectron spectroscopy (SRPES). For the lightly Sidoped GaAs(001) surface, PL measurements reveal that after heating to 500 °C a layer with lower PL peak intensities related to gallium vacancies than those of the bulk exists just under the thermal degraded layer. SRPES shows that EFs moves upward to 1.1-1.17 eV above

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... the valence band maximum when this thermal degraded layer is removed by chemical etching. The excess arsenic on the surface, which is formed by rinsing the etched surface with deoxygenated and deionized water, is evaporated by heating in ultra-high vacuum (UHV). After evaporation of excess arsenic on the surface by heating, the etching-depth dependence of EFs for a sample pre-heated in UHV correlates with the existence of this defect concentration layer. These results suggest that the position of EFs for GaAs(001) surface is strongly influenced by crystal defects near the surface.