Reflectance-anisotropy spectroscopy and surface differential reflectance spectra at the Si(100) surface: Combined experimental and theoretical study

Abstract

We present reflectance-anisotropy spectroscopy ͑RAS͒ and surface differential reflectivity ͑SDR͒ experiments carried out on well-characterized single-domain nominal silicon ͑100͒ surface at room temperature. The results are compared with first-principles calculations which include many-body effects, namely, self-energy and excitonic effects. These strongly modify the line shape of the optical spectra. For a set of the five measurements, the RAS of clean, monohydride, and dyhidride surfaces, and the corresponding SDRs, good agreement between theory and experiment is obtained only when, in the calculation, the electron-hole interaction is accounted for.

Optical and phonon excitations of modified Pandey chains at the Si(111)-2×1 surface

“…A similar approach is commonly adopted when DFT calculations are used to compute optical spectra without inclusion of many-body effects-conduction bands are simply shifted upward until optimal agreement with experiment is achieved. 28 In the present work the shift occurs because Fock exchange has been included in the exchange correlation functional and wave functions and energy eigenvalues are obtained self-consistently.…”

“…The RAS spectrum below 1 eV is a single, asymmetric peak with a sharp leading edge. The optical response of this surface is highly anisotropic, being very large parallel to the π chains and very small perpendicular to the chains in the infrared [compared to, for example, the Si(100)-2×1 surface 28 ]. In the visible region (between 2 and 4 eV) the imaginary part of the surface susceptibility perpendicular to the π chains is greater than that parallel to the chains.…”

Optical in situ monitoring of hydrogen desorption from Ge(100) surfaces

“…The origins of the RAS signals can be identified either by ab initio calculations, 19,20 modeling, 21 or by correlation of RAS signals to results from other surfacesensitive techniques. 22 Therefore, RAS signals provide control and understanding of processes on the sample surface during preparation in any process gas ambient.…”

Probing surface and interface structure using optics

“…Including the electron-hole interaction clearly shifts the spectral structure at low energies, improving the agreement with experiment but, at higher energies, agreement is not so good, probably because of convergence problems due to the limited sampling of k-space currently possible [56]. It is likely that these sophisticated calculations will become more common, given the increasing interaction between surface optics experimentalists and theoreticians, which is being encouraged by initiatives such as the European Theoretical Spectroscopy Facility (http://www.etsf.eu/).…”

“…However, for optical transitions the electronhole interaction and local-field effects should also be taken into account and this requires efficient ways of solving the Bethe-Salpeter equation (BSE) [55]. Results of state-ofthe-art calculations are shown in figure 10 for the Si(001)-c4 × 2 structure, which is the room temperature equilibrium structure where the dimer rows of the Si(001)-2 × 1 surface are buckled [56].…”