Negative differential conduction in the Bloch oscillations regime in the hexagonal silicon carbide polytypes 4H, 6H and 8H

The paper discusses an experimental demonstration of Bloch oscillations connected with Bragg reflection of electrons from the first miniband edge in superlattices of different silicon carbide polytypes. The original experimental method was geared towards obtaining a strong uniform electric field meeting the conditions of Bloch oscillations. Direct measurements have allowed observation of the negative differential conduction associated with the Bloch oscillations for polytypes 4G, 6H and 8H, having superlattice constants 5, 7.5 and 10 Angstrom respectively. The most recent result is the negative differential conductance for polytype 8H, which is of special interest since it correlates well with the previously obtained data for 4H and 6H polytypes. In fact, the threshold electric fields of negative differential conductance are 290, 150 and 110 kV cm(-1) for polytypes 4H, 6H and 8H respectively. These data, taking into account the difference of the superlattice periods, are in good agreement with the criteria for the Bloch oscillation phenomenon. (C) 1998 Academic Press Limited.