Visible light-emitting diodes either with a structure of glass/ITO/

p

a-SiC:H/

i

a-SiC:H/

n

a-SiC:H/Al or with a structure of glass/ITO/a-SiC:H/Al have been developed by the glow discharge deposition in SiH

4

+CH

4

mixture. The

p-i-n

LEDs exhibit characteristics of switching diode with turn-on voltage of about 16V

while the another type of LED exhibits characteristics of avalanche breakdoswn in a uniform medium with threshold field of about 1.5×10

8

V/cm. The two types of aSiC:H thin film LEDs named injection LED and impact ionization LED

respectively

emit visible white light when their own critical conditions are established. Both of them have a broad lightemission band centred around 2.0eV and extend over the whole visible range. The peak energy of injection LED's spectrum does not change as the injection current increases

but the peak energy of the impact ionization LED's spectrum changes from 1.87 eV to 2.04 eV when the avalanche current increases from 0.15mA to 6mA. The optical gap of a-SiC:H thin films

including either

n

-or

p

-doped layers

is maintained at 2.2 eV by adjustments of the deposition parameters and measured according to Tauc plot. The irradiation recombination mechanizm concerned with these LEDs is suggested to be a transition between the extended states in conduction-band and the localized states in valence-band tail.The variation of peak energy of the impact ionization LED's spectrum is attibuted to the energy distribution of excess electrons in conduction-band

which is dependent on the excitation voltage.