P. Jiříček

Polarity of semipolar wurtzite crystals: X-ray photoelectron diffraction from GaN{101¯1} and GaN{202¯1} surfaces

Polarity of semipolar GaN(101¯1) (101¯1¯) and GaN(202¯1) (202¯1¯) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80–100° from the 〈0001〉 normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN{101¯1} and GaN{202¯1} crystals if referred to 〈0001〉 crystal axes. For polarity determinations of all important GaN{h0h¯l} semipolar surfaces, the above given polar angle range is suitable.

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.

Photoemission from Al(100): experiment and one-step theory

Experimental and theoretical study of angle resolved photoemission from the Al(100) surface is presented. Photoelectron spectra are calculated with an ab initio one-step theory of photoemission within the augmented plane wave formalism and are found to be in excellent agreement with the experiment. The lifetime of the (100) surface state and the photon energy dependence of the intensity of photoemission from the surface state are determined. The treatment of inelastic scattering by the optical potential within the one-step theory perfectly describes the surface sensitivity of the photoemission from Al(100) for energies up to 100 eV.