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 ef fect and Franz-Keldysh oscillations) in the photoionization cross sect ion of semiconductor impurities are studied in presence of two factors relevant to experimental measurements: the electron-phonon polar coup ling and a Linear spatial variation of the applied electric field. Imp ortant for EI-VI and III-V semiconductors, the electron-phonon polar c oupling is treated using an approach adapted from the classical work o f Huang and Rhys. Our calculations show that the Franz-Keldysh oscilla tions should be visible even in the presence of the electron-phonon in teraction for shallow impurities, For deeper impurities, the oscillati ons should be visible if the electron-phonon coupling is weak, which i s unlikely to happen in II-VI semiconductors. We also show that a line ar spatial variation of the applied electric field leads to modificati ons of much smaller amplitude. (C) 1995 American Institute of Physics.