Wannier-Stark localization in the natural superlattice of silicon carbide polytypes

Results of a study of silicon carbide polytypes under high electric fields are presented. The presence of a natural superlattice in silicon carbide polytypes is shown to introduce a miniband structure into the conduction band, which leads to a number of effects: negative differential conductivity in the Bloch oscillation mode, electron-phonon resonances, localization in the lower miniband, resonance tunneling between the first and second minibands, prevalence of holes in the impact ionization in a wide range of fields, anomalously high avalanche breakdown fields (with a negative temperature dependence of the breakdown field) and other unusual effects. Notice that all the phenomena mentioned above are parts of a single Wannier-Stark localization process, which sets in as the mean electric field increases from 100 to 2900 kV/cm (the maximal field magnitude achieved in an abrupt p-n junction is twice larger).