BOUND POLARONS IN ASYMMETRIC QUANTUM-WELLS IN AN ELECTRIC-FIELD

We have proposed the Hamiltonian of a polaron bound to a donor impurit y in semiconductor quantum wells (QWs) in the presence of an electric field, The couplings of an electron with the confined bulk-like Longit udinal optical (LO) phonons, half-space LO phonons and interface phono ns are considered. In particular, the interaction of the impurity with the various phonon modes is also included. We have calculated the ion ization energy of a bound polaron in AlxlGa1-xlAs/GaAs/AlxtGa1-xtAs as ymmetric and symmetric QWs. Results are obtained as a function of the barrier height (or equivalently of Al concentration x), the well width , the electric field intensities and the position of impurity in the Q Ws. Our numerical calculations show clearly that the interaction betwe en the impurity and the phonon field plays an important role in screen ing the Coulomb interaction. It is shown that for a thin well (<12nm), the cumulative effects of the electron-phonon coupling and the impuri ty-phonon coupling can contribute appreciably to the donor ionization energy and polarizability.