REPRESENTATION OF FRANZ-KELDYSH EFFECT BY SPECTRAL BROADENING

An approximate general treatment is given for the effect of electric field on the absorption edges of insulating crystals, taking into account electron-hole and carrier-lattice interactions. Using a representation in which the electric field appears in the equations of motion as a force term, low angle scattering is treated by an adiabatic approximation. These scattering processes modify the optical absorption in a complicated way, but the field effect can be represented by a broadening of the actual zero field spectrum. No comprehensive account is attempted for localized states in a field, but it is indicated that in many cases the spectral broadening description of the field effect can be retained for transitions involving localized states. Band anisotropy, lifetime broadening and surface effects are considered in the analysis. The predictions of the theory are compared briefly with published experimental results. © 1968.