M. Cukr

Angle - resolved photoemission study of two phases of the GaAs(100)-c(4×4) surface

We prepared two surface phases of the Ga(001)-c(4×4) reconstruction (α, β) by molecular beam epitaxy (MBE) using As4 and As2 molecular beams and examined the surfaces by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and core level photoelectron spectroscopy with the synchrotron radiation as the excitation source. It is demonstrated that the photoelectron spectroscopy can distinguish between the phases. Appearance of intensive surface state 0.5 eV below the top of the valence band at lower energies is linked to the presence of the β-phases on the surface while in the α-phase spectra the peak is missing. Both As 3d and Ga 3d photoelectron lines show substantial differences between the phases in line shapes as well as in their deconvoluted components. The 3d data are in agreement with different surface composition and atomic structure of both phases.

A theoretical investigation of photoemission spectra from (GaAs)2(AlAs)2 superlattices

Abstract We calculated photoemission spectra within the one-step model for the (001) surface of the (AlAs) 2 (GaAs) 2 superlattice structure. The purpose is to discriminate between spectral features which are caused by the surface, and those which are characteristic properties of the superlattice. Direct transitions indicate the opening of band gaps at the Brillouin zone edge, which are characteristic for the modified periodicity of the superlattice. Furthermore, the layer resolved photocurrent shows that one can also identify excitations from AlAs which are hidden below the first two GaAs layers and from As atoms at the boundary between the different semiconductors. Furthermore, emissions from surface states and resonances are also recognized.