Electroreflectance of GaAs and GaP to 27 eV using synchrotron radiation

Electroreflectrance (ER) spectra of GaAs and GaP, taken with the Schottky-barrier method, exhibit to 27 eV the strong structural enchancement and high resolution characteristic of similar measurements below 6 eV. Above 20 eV, a new set of critical points is observed between the flat valence bands derived from the Ga 3d core levels and the local extrema of the sp3 conduction bands. The attained resolution, of the order of 100 meV, enables us to resolve clearly the spin-orbit splitting of 0.45 eV of the 3d-derived valence bands. The following critical-point energies have been determined in GaAs and GaP, respectively. sp3 valence conduction: E1′, 6.63 ± 0.05 eV, and 6.80 ± 0.05 eV; E1′+Δ1′, 6.97 ± 0.05 eV (GaAs only); E0\u27\u27(Γv15→Γc12), 10.53 eV, and 9.38 ± 0.1 eV; E0\u27\u27\u27(Γv15→Γc1), 8.33 ± 0.1 eV, and 10.27 ± 0.1 eV, E1\u27\u27, 9.5 ± 0.2 eV, and 10.7 ± 0.2 eV. E5, E6, and E7 structures are observed at 15.1, 16.7, and 17.9 eV in GaAs, and at 14.7, 16.1, and 18.6 eV in GaP. Relative values of 3d core to sp3 conduction-band matrix elements are estimated for several states and show that the lowest 3d core-level ER structures arise from transitions terminating at the Xc1conduction-band minimum. We calculate an exciton or core-hole interaction shift of 150 meV for GaP and 200 meV for GaAs, which indicates that core-hole effects are probably small for these materials. Spectral features with initial structure less than 100 meV in width are observed above 20 eV, showing that broadening effects are much smaller in this energy range than previously believed

Ordering and Absolute Energies of the L6c and X6c Conduction Band Minima in GaAs

Resolved critical point structures in Schottky-barrier electroreflectance spectra of Ga3dV-sp3 conduction band transitions in the 20-22-eV range provide a direct proof that the L6C equivalent minima lie approximately 170±30 meVbelow the X6C minima in GaAs. This ordering, opposite to that assumed and apparently supported by previous experiments, is in fact consistent with these experiments and provides natural explanations for many formerly puzzling features of GaAs

Line shape and symmetry analysis of core-level electroreflectance spectra of GaP

No dependence of electroreflectance line shapes upon polarization direction or crystal orientation is found for any core-level electroreflectance structure from the Ga 3dv core levels to the conduction bands in GaP. Matrix-element effects that are responsible for anisotropy in sp3 valence-conduction-band electroreflectance spectra appear to be too weak to be detected in core-level spectra. The result may be general. The field-induced modulation line shape, Δε1, for the Ga 3dv32,52−Xc6 critical points is obtained from the dependence of the spectra and the generalized Seraphin coefficients upon angle of incidence. The line shape is further analyzed to obtain the Δε1 spectrum for Ga 3dv52−Xc6 alone. This procedure yields a spin-orbit splitting Δ3d=0.43±0.02 eV. A weighting of 0.65 ± 0.05 is also obtained for the j=32band relative to the j=52 band. This is in good agreement with the 4:6 ratio expected on d-band occupancy, showing that the matrix elements are also independent of j. The line shape of Δε1 is in good agreement with that predicted by the lifetime-broadened, Coulomb-enhanced Franz-Keldysh theory given by Blossey. The line shape shows a broadening of 160 meV for this transition, and a momentum matrix element about 1/3 as large as that characteristic of sp3 valence-conduction-band transitions

Modulation spectroscopy at non‐normal incidence with emphasis on the vacuum‐uv spectral region

Expressions are given to analyze modulation spectra taken at non‐normal incidence. These expressions are used to determine the optimum angle of incidence to maximize the signal‐to‐noise ratio. Significant improvements are shown to be obtained in the vacuum‐uv spectral region by making measurements at relatively large angles of incidence. We apply these expressions to evaluate the field‐induced change in the dielectric function for the 20.5–21.0‐eV core‐level doublet in GaP from Schottky‐barrier electroreflectance data. The line shape obtained is consistent with that of a field‐modulated M 0critical point modified by a Coulomb attraction between the core hole and the excited electron

Electroreflectance of GaSb from 0.6 to 26 eV

Schottky barrier electroreflectance spectra are reported for GaSb from 0.6 to 26 eV. Accurate energies are determined for a number of critical points between the sp3 and Ga−3d valence bands and the conduction bands. The energy of XV7 is shown to lie at least 3 eV below ΓV8. This is below the value obtained from local pseudopotential calculations and the x-ray photoemission assignments, but follows a trend previously established by nonlocal pseudopotential calculations for Ge and GaAs. The Ga 3d-XC6 exciton binding energy is of the order of 100 meV

Temperature Coefficients of Energy Separations between Ga 3d Core Levels and sp3 Valence-Conduction Bands in GaP

The measured temperature coefficients of the energy separations between the Ga 3d core levels and the top (Γ8V) and bottom (X6C) of the sp3 valence and conduction bands in GaP between 110 K and 295 K are (+1.0±0.5)×10−4 eV K−1and (-2.4±0.5)×10−4 eV K−1, respectively. They are described within experimental accuracy by the Debye-Waller, hydrostatic, self-energy, and spatially averaged screened-ion core potential interactions of the sp3 bands alone. No significant core-level contribution is observed

Direct Determination of Sizes of Excitations from Optical Measurements on Ion-Implanted GaAs

Using a simple model that describes the decrease of the amplitudes of optical structures in ion-implanted crystals, projected areas of several valence and core excitons in GaAs are determined. The last remnant of crystal-related optical structure vanishes for crystallite areas less than (16Å)2

Electron-Core-Hole Interaction in GaAsP

The electron-core-hole interaction is studied via energy derivative reflectance spectra of 20-eV transitions from Ga 3dcore levels to lower conduction-band final states in GaAs1−xPx alloys. A two-level anticrossing behavior of line shapes and threshold energies as the relative positions of the L and X minima invert yields a previously unanticipated L−Xmixing energy |VLX|∼50 meV

Follow the light : Ellipsometry and polarimetry

[No abstract available]Original Publication:Hans Arwin and D.E. Aspnes, Follow the light: Ellipsometry and polarimetry, 2009, Physics Today, (62), 5, 70-71.http://dx.doi.org/10.1063/1.3141950Copyright: American Institute of Physicshttp://www.aip.org