Germanium is an indirect bandgap semiconductor having its onset of absorption at 0.8 eV at room temperature. Knowledge of the behavior of critical points (CPs) of Ge and other semiconductors is valuable for the further development of electronic and optoelectronic devices. The dielectric function of Ge has been measured between 0.5 eV and 1.3 eV using spectroscopic ellipsometry at various temperatures between 10 K and 740 K. The interband CPs E0 and E0+∆0, where E0 is the direct band gap of Ge and ∆0 is the spin-orbit splitting occurring at the center of the Brillouin zone, lie in this energy range and are subject of our investigations. Applying an analysis in reciprocal space by performing a discrete Fourier transform of the data points and fitting the resulting Fourier coefficients, the parameters describing the line shape of E0 are found as a function of temperature. Like for the CPs at higher energies, the authors find a red shift of the E0 and E0+∆0 energies which can be described by a Bose-Einstein factor taking into account electron-phonon interactions. The results of the reciprocal-space analysis are compared to the parameters determined by a parametric semiconductor fit.
APS March Meeting Abstracts
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