The effect ofex situhydrogen passivation process on the performance of visible hydrogenated amorphous silicon carbide (a-SiC:H)-basedp-i-ntype thin-film light-emitting diodes has been investigated. Anex situhydrogen passivation process dramatically improved the device performance; that is, the threshold voltage decreased by about 5 V, the electroluminescence (EL) intensity increased by a factor of about 3, and the EL peak shifted toward a short wavelength from 700 to 600 nm, resulting in an increase of the brightness from 1 cd/m2to 35 cd/m2. This improvement of device performance is caused by the passivation of interface states in thep/iandi/ninterfaces as well as midgap states in the luminescent active intrinsica-SiC:H layer by hydrogen atoms. A process time dependence of theex situhydrogen passivation effect on the device performance also has been studied. ©1997 American Institute of Physics.