A hydrogenated amorphous-carbon (a-C:H) active-layer carrier-injection type thin-film light-emitting diode (TFLED) with a very low threshold voltage of 3.5 V was fabricated for the first time using a photochemical vapor deposition method. Compared to an intrinsic hydrogenated amorphous silicon carbide active layer TFLED, its electroluminescence (EL) spectrum peak shifted from 720 nm to 600 nm without hydrogenation of the intrinsic film or interface (p/i or i/n) band grading. This blue shift is caused by the band gap widening from 2.4 eV for a-SiC:H to 3.2 eV for a-C:H. The current transport mechanism of the TFLED could be explained by the ohmic current near the subthreshold voltage region and the Fowler-Nordheim tunneling current over the threshold voltage.

Ultrasound treatment ͑UST͒ applied at room temperature enhances electroluminescent intensity ͑maximum at 600 nm͒ and optical output in thin-film light-emitting diodes with hydrogenated amorphous-carbon as an active layer. This positive UST effect is attributed to a reduction of the diode series resistance caused by a change of the interface and contact resistances. The UST effect is saturated with increase of the ultrasound amplitude.