Rudiger Lange

Dielectric response of strained and relaxed Si1−x−yGexCy alloys grown by molecular beam epitaxy on Si(001)

Using spectroscopic ellipsometry, we measured the pseudodielectric function of Si1−x−yGexCy alloys (0≤x≤0.48,0≤y≤0.05) grown on Si(001) using molecular beam epitaxy. For pseudomorphically strained layers, the energy shifts of the E1, E1+Δ1, E0′, and E2 transitions are determined by line shape analysis and are due to alloy composition effects, as well as hydrostatic and shear strain. We developed expressions for hydrostatic and shear shift from continuum elasticity theory, using deformation potentials for Si and Ge, for biaxial stress parallel to the (001) growth plane in a diamond or zinc blende‐type crystal and applied this to the ternary Si–Ge–C alloy. The energies of E1 and its spin‐orbit split partner E1+Δ1 agree fairly well with theory. The E2 transitions in Si1−xGex at around 4.3 eV depend linearly on Ge concentration. In case of relaxed layers, the E1 and E1+Δ1 transitions are inhomogeneously broadened due to the influence of misfit and threading dislocations. For a silicon cap on top of a dislocat...

Dielectric response of thick low dislocation-density Ge epilayers grown on (001) Si

Spectroscopic ellipsometry was used to measure the dielectric functions of epitaxial and bulk Ge at photon energies from 1.5 to 5.2 eV. The epitaxial Ge was grown at 400 °C by molecular beam epitaxy on (001) Si substrates. The optical response and the interband critical‐point parameters of Ge on Si were found to be indistinguishable from that of bulk single crystal Ge, indicating high optical quality. Dislocation density measurements using an iodine etch verified low surface defect densities. We conclude that epitaxial Ge grown on Si at relatively low temperatures is suitable for optical device applications.

Theoretical and experimental determination of optical and magneto-optical properties of LuFe2 single crystal

Abstract We have studied the diagonal and off-diagonal optical conductivity of a LuFe2 single crystal grown by the flux method. Using spectroscopic ellipsometry we have measured the dielectric function from 1.5 to 5.5 eV. The magneto-optical parameters (Kerr rotation and ellipticity) from 1.4 to 4.0 eV were obtained using a magneto-optical polar Kerr spectrometer at temperatures between 7 and 295 K and applied magnetic fields up to 1.2 T which fully saturates the magnetic moment of LuFe2. We describe the apparatus and evaluate the off-diagonal conductivity components from the data. Theoretical calculations of optical conductivities and magneto-optical parameters were performed using the tight binding-linear muffin tin orbitals method within the local spin density approximation. When lifetime broadening is included, the calculations agree well with the experimental data.

Optical properties and band structure of Ge1−yCy and Ge-rich Si1−x−yGexCy alloys

Abstract We measured the dielectric function of Ge1−yCy and Ge-rich Si1−x−yGexCy alloys from 1.6 to 5.2 eV using spectroscopic ellipsometry. These alloys were grown by molecular beam epitaxy at 600°C on (001) Si substrates. Analytic lineshapes fitted to numerically calculated derivatives of their dielectric functions determined the critical-point parameters of the E1, E1+Δ1, E0′, and E2 transitions. The critical-point energies of the Ge1−yCy alloys were found to be indistinguishable from those of bulk Ge. This indicates that the presence of C in these alloys has no detectable influence on the band structure. The amplitude of the ellipsometric spectra is much lower than for bulk Ge, which can be attributed to surface roughness and explained within the framework of the Kirchhoff theory of diffraction or using effective medium theory. The degree of surface roughness indicated by optical measurements was verified by atomic force microscopy.

Comment on ``Optical Characterization of Si 1 - xCx/Si (0=< x =<0.014) Semiconductor Alloys"

Based on the previous comment by Zollner et al., we discuss the possibility that the double feature in the derivative spectra of the dielectric functions of Si 1-x C x /Si (0 ≤ x ≤ 0.014) and Si 0.924-x Ge 0.076 C x /Si (0 ≤ x ≤ 0.014) alloys grown using solid phase epitaxy may come from interference phenomenon. We emphasize that the argument does not change the main content of our previous reports.