Terahertz emission from SiC natural superlattices in strong electrical field

摘要

Results are reported from a study of the terahertz electroluminescence from 8H-, 6H-, and 4H-SiC natural superlattices under the action of an electrical field applied along the natural superlattice axis. It is shown that the single, relatively narrow emission lines (L1-lines) dominate in the electroluminescence spectrum at moderate bias voltages and follow the increase of the width of the first mini-band of the superlattice in accordance with the criterion for Bloch oscillations. At bias voltages well above the Bloch oscillation threshold, the structure of the terahertz emission spectra undergoes considerable changes, which occur due to the appearance of a new intense, broader emission line (L2-line) with a maximum at about 12-13 meV. Tentatively, this latter emission is attributed to optical transitions between Wannier-Stark ladders formed from degenerate states in a side minimum of the SiC conduction band under strong electric field conditions.