The interaction of electrons with polar-optical phonons in two- and three-dimensional electron systems

The influence of the polar-optical interaction on the electronic energy levels at high magnetic fields has been investigated for two- and three-dimensional electron systems in weakly polar semiconductors. The interaction leads to a resonant splitting of the energy levels. For a three-dimensional syste m the well-known perturbation theoretical approaches have been compared with variational calculations. An improved Wigner-Brillouin-like perturbation theory has been developed which describes the polaron effects far away as well as in the resonance with high accuracy. For the two-dimensional electron systems a variational non-parabolicity model has been developed to describe the band structure. The influence of the electric and the magnetic potential on the energy levels is described analytically. The broadening of the Landau levels by ionizing impurity scattering and the cyuclotron resonance linewidth has been calculatd. The experimentally observed oscillation of the linweidth with the filling factor of the Landau levels can be well attributed to the variation of the screening strength. The influence of the distribution of the scattering centers with respect to the inversion layer has been calculated, which allows the determination of the material quality. The polaron interaction in two-dimensional electron systems has been first calculated in single-particle interaction for the zeroth and the first electric subband. The influence of the dynamic screening on the interaction strength has been investigated and a dependence on the filling factor as well as on the levelwidth was found. (Author)