Papers by Author: Alla A. Lepneva

Abstract: A natural superlattice (NSL) in silicon carbide polytypes is shown to introduce a miniband structure into the conduction band, which leads to depressing of the electron impact zone-zone ionization at 300K with the electric field directed along the crystal axis or the NSL axis. The NSL influence can be also observed in the nitrogen impact ionization at 4.2K. In this case for the parallel field the impurity breakdown has not been fixed up to the fields 1.6 MV/cm in 6H-SiC. These results are explained by the insufficient gain in miniband for the ionization electron energy. Therewith the impurity breakdown at the electric field perpendicular to this axis correlates with a classical picture.

Abstract: In this work, we have studied I-V characteristics of Al breakdown in 6H-, 4H- and 15R-SiC in electrical field. As a result there obtained the next original data: 1) decreasing dependence of breakdown field due to the concentration increase in the range of Na – Nd = 5x1017–1019 cm-3; 2) absence of low temperature breakdown when Na - Nd< 1017 cm-3; 3) increasing of breakdown field while temperature declines from 77K to 4.2K; 4) at 300K the breakdown field decreases and the breakdown takes place in samples with the absence of low temperature breakdown; 5) gigantic enhancement of breakdown field at F||C. 6) the theoretical analysis based on the theory of a zero radius potential supports the probability of breakdown field enhancement at F||C.

Abstract: In materials with a small degree of ionicity ranging 10-15%, such as in SiC, carrier scattering on polar optical potential is possible. Unlike scattering on deformation potential, the drift mobility in this case increases continuously. As this phenomenon may be realized in SiC hot hole transport, I-F characteristics in 6H-SiC with Na-Nd ~ 5x1017 cm-3 have been studied at electrical field 1-150 kV/cm for temperature from 300 to 600K. Furthermore, we studied the breakdown of Al impurity.

Abstract: A natural superlattice (NSL) in silicon carbide polytypes is shown to introduce a miniband structure into the conduction band, which leads to a number of effects in phenomena of quantum-mechanical transport and impact ionization when the electric field directed along an axis of NSL (axis C in crystal). These processes are absolutely traditional when the electric field is perpendicularly to this axis. The parallel field phenomena are explained by the effects of the Wannier–Stark localization (WSL) among them the Bloch oscillations effect is most prominent today.