IMPURITY PHOTOIONIZATION IN THE PRESENCE OF A STATIC ELECTRIC-FIELD - PHONON COUPLING AND NONUNIFORM ELECTRIC-FIELD EFFECTS

The modifications induced by a static electric field (Franz-Keldysh effect and Franz-Keldysh oscillations) in the photoionization cross section of semiconductor impurities are studied in presence of two factors relevant to experimental measurements: the electron-phonon polar coupling and a Linear spatial variation of the applied electric field. Important for EI-VI and III-V semiconductors, the electron-phonon polar coupling is treated using an approach adapted from the classical work of Huang and Rhys. Our calculations show that the Franz-Keldysh oscillations should be visible even in the presence of the electron-phonon interaction for shallow impurities, For deeper impurities, the oscillations should be visible if the electron-phonon coupling is weak, which is unlikely to happen in II-VI semiconductors. We also show that a linear spatial variation of the applied electric field leads to modifications of much smaller amplitude. (C) 1995 American Institute of Physics.