By combining reflectance spectroscopy and spectroscopic ellipsometry, the complex dielectric function of SrTiO, in the frequency range 40-5000 cm-' at 20, 100, 200, and 300 K has been determined. Using a factorized description, analytical expressions for the optical quantities were derived, giving excellent agreement with the experimental data. These can be used for two-layer fits of films on SrTiOs, e.g., of high-T, superconductors. The fit parameters complement very well those found at higher temperatures. 0 1995 American Institute of Physics.
We have used spectroscopic ellipsometry to measure the dielectric function e (u) of GaP from 10 to 640 K in the 1.6 -5.6-eV photon-energy region. By performing a line-shape analysis of the observed structures, the interband critical-point (CP) parameters (strength, threshold energy, broadening, and excitonic phase angle) and their temperature dependence have been determined. Special emphasis is put on the Eo Eo + &0 and E'2 CP's. We determine the spin-orbit splitting of I'i5 to be &o=160+10 meV. The observed decrease in energy of the CP's (after correction for the effect of thermal expansion) and the corresponding increase in broadening with increasing temperature agree reasonably well with results of a calculation that takes into account the Debye-Wailer and self-energy terms of the deformation-potential-type electron-phonon interaction. New local empirical pseudopotential form factors were fitted to the available band-structure data and used in the electron-phonon calculations.
The three independent components of the piezo-optical tensor P,~I,~(u) have been determined in uniaxially stressed Si using rotating-analyzer ellipsometry. This tensor, with only three complex independent components in the case of Si, links the changes in the real and imaginary parts of the dielectric tensor Ae, s(w) to an arbitrary stress X=Xq~[i.e. , De,~(ur) = P~&I, (w)Xq~]. Using the experimental values of P,sq~(~), several related functions and parameters were derived and compared with previous piezoreflectance, ac-stress-modulated reflectivity, Raman spectroscopy work, and theoretical estimates. Deformation-potential constants for the optical transitions between 3 and 4 eV were obtained using the ellipsometric data. In addition, the diferent components of the piezooptical tensor were calculated using the empirical pseudopotential method and reasonable agreement between theory and experiment was found. Our data also clarify previous problems and errors in the existing literature.
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