Interband Electro-Optical Properties of Germanium. II. Electroreflectance

By modifying the experimental conditions of the semiconductor-in-electrolyte electroreflectance technique we have been able to obtain the flat-band condition at the surface and therefore obtain results which can be simply interpreted. In particular, it is shown that the Kramers-Kronig transforms of the electroabsorption experiments of the previous paper, where the field is known and uniform, agree quite well with our new electroreflectance data at the direct edge of germanium. The agreement between the two methods allows a direct determination of the effective electric field in the electroreflectance experiments. It is found that the effective electric field is directly related to the average penetration depth of the photons and therefore explains the increasing width of the electroreflectance lines with energy, observed in all previous experiments. Detailed analysis of the 2.1- to 2.3-eV peaks under these new experimental conditions shows that they are not necessarily the result of spin-orbit splitting and may arise from many different parts of $k$ space.