On the nature of E1‐transitions in germanium

Abstract

AbstractThe E1 optical structure of Ge is studied by unmodulated, first‐derivative, and low‐field electroreflectance spectra. An extensive investigation of heavily doped samples shows only minor changes of their electron structure for impurity concentrations up to 6 × 1019 cm−3. As the freecarrier plasma screens the electron–hole interaction, exciton effects are reduced owing to the doping. While the exciton interaction is found to modify the electroreflectance lineshapes, its role is not essential in unmodulated and first‐derivative ones. The lineshape analysis of the room temperature spectra shows that the E1‐structure is not well described by a simple parabolic critical point of the joint density of states, except for the low‐field electroreflectance, which is fitted satisfactorily by a two‐dimensional minimum (substituting a rather complex band structure with at least one M1 saddle point).