A criterion for the validity of the uniform-field approximation in electroreflectance experiments is derived and discussed. It is shown that a proper choice of impurity concentration can minimize the inhomogeneity for a given magnitude of the electric field. Using germanium as an example, the optimum doping levels are given for various values of the electric field. These optimal impurity concentrations minimize the mixing of the real and imaginary parts of the change in the dielectric function with electric field, so that the observed line shapes can be easily interpreted. The results show that the uniform-field approximation can be used with electric as high as ${10}^5$ V/cm, provided the proper doping levels are used.

• Received 14 April 1969

DOI:https://doi.org/10.1103/PhysRev.187.1182