Various light-emitting diodes of 6H-SiC, doped in the n layers with Al, Ga, or B acceptors and N donors, have been fabricated using a rotation dipping technique. A detailed study of electroluminescence mechanisms from ∼100 to 400 K has been carried out using photoluminescence, electroluminescence, and time-resolved spectra. At low temperatures the radiation originates mainly in the p layer, and around room temperature in the n layer. The luminescence mechanisms are free-exciton recombinations for the peak at ∼425 nm, donor-acceptor pair recombinations for the main broad band, transitions within localized centers for the peak at ∼455 nm, and recombinations due to divacancies for the series of peaks beginning at ∼470 nm. The dependence of the electroluminescence efficiency on the N concentration in the n layers is studied and methods to improve efficiency are discussed. The maximum external quantum efficiencies obtained were 1.2×10-5 for Al-doped, 9×10-6 for Ga-doped, and 2.5×10-5 for B-doped diodes, and were improved by a factor of 2 by using an epoxy coating.
