Low Temperature Electro-Reflectance Spectra of Germanium in Spectral Region from 0.7 to 2.6 eV

Abstract

Electro-reflectance spectra of germanium in photon energies from 0.7 to 2.6 eV have been investigated in the temperature region between 300°K and 24°K. The measurements have been performed by modulating the interface potential of germanium-tin oxide junction, which enables low temperature electro-reflectance experiment down to liquid helium temperature. The line shapes obtained abound \(\varGamma_{25'}-\varGamma_{2'}\) transition edge are in good agreement with that expected from the theory except that a little discrepancy by the effect of exciton exists near the edge. In the spectral region from 2.0 to 2.6 eV, the spectra observed at low temperatures exhibit very fine structures as compared with that obtained at room temperature. These structure are explained as the electro-optical signals associated with M 1 critical point having both parallel and transverse types, including a Lorentzian broadening, and attributed to \(\varLambda_{3}-\varLambda_{1}\) transition and its spin-orbit band edges. Temperature dependences of the peak positions related to the critical points are discussed