GEOMETRIC ORDERING, SURFACE-CHEMISTRY, BAND BENDING, AND WORK FUNCTION AT DECAPPED GAAS(100) SURFACES

We present a comprehensive study of epitaxially grown and A s-coated GaAs(100) surfaces as a function of As desorption temperature and background pressure We have used low-energy electron diffraction to determine surface reconstruction, and core-level a nd valence-band soft-x-ray photoemission spectroscopy to perform chemical and electronic characterization of these surfaces. We find gradual changes in surface geometry and composition, and a limited (approximately 120 meV) Fermi-level movement over numerous reconstructions in the 250-650-degrees-C annealing temperature range. The surface ionization potential and work function exhibit large changes between different surface reconstructions. In conjunction with other techniques, work-function measurements present evidence of surface inhomogeneity for many of the desorption temperatures and surface reconstructions. This inhomogeneity appears related to the existence of differently reconstructed patches on the surface. Our results emphasize the complexity of reconstructed GaAs(100) surfaces and the advantages of a multiple-technique approach for their characterization.