FERMI-LEVEL INHOMOGENEITIES ON THE GAAS (110) SURFACE IMAGED WITH A PHOTOELECTRON MICROSCOPE

A photoelectron microscope operating with a retarding field analyzer can exploit core level energy shifts in order to image Fermi-level variations of semiconductor surfaces. Fermi-level maps of cleaved n- and p-type GaAs (110) resolved to better than 10-mu-m indicate lateral variations in the surface Fermi level which are often quite abrupt. In agreement with earlier, lower resolution work [J. M. Palau, E. Testemale, and L. Lassabatere, J. Vac. Sci. Technol. 19, 192 (1981)],1 Fermi-level topography is found to be highly correlated with surface roughness as characterized by scanning electron microscope (SEM), optical microscope, and stylus profilometer. Defective fracture surfaces have two distinct characters within SEM resolution: linear defects (steps and ledges) that may extend over millimeters and smooth glassy areas. Both types of surface defects shift the Fermi level towards midgap. The largest defect derived pinnings encountered to date result in the Fermi level lying 0.5 eV above the valence-band maximum for both n- and p-type GaAs. Submonolayer In evaporations reduce Fermi-level variations by shifting surface Fermi levels in formerly unpinned regions into the gap.