Direct Verification of the Third-Derivative Nature of Electroreflectance Spectra

The electric-field-induced change in the linear dielectric function for the $E_1$ and $E_1+{\Delta }_1$ transitions of Ge, determined from low-field electroreflectance measurements, is shown to be in quantitative agreement with the third derivative of the linear dielectric function measured by high-resolution ellipsometry techniques. This result relates electroreflectance spectra to other types of modulation spectra and provides the first direct verification of the nonlinear optical interpretation of electroreflectance.