The present infra-red light-emitting device includes a substrate with a
first window layer, a silicon dioxide layer positioned on the first
window layer, silicon nanocrystals distributed in the silicon dioxide
layer, a second window layer, a transparent conductive layer and a first
ohmic contact electrode positioned in sequence on the silicon dioxide
layer, and a second ohmic contact electrode positioned on the bottom
surface of the substrate. The present method forms a sub-stoichiometric
silica (SiO.sub.x) layer on a substrate, wherein the numerical ratio (x)
of oxygen atoms to silicon atoms is smaller than 2. A thermal treating
process is then performed in a nitrogen or argon atmosphere to transform
the SiO.sub.x layer into a silicon dioxide layer with a plurality of
silicon nanocrystals distributed therein. The thickness of the silicon
dioxide layer is between 1 and 10,000 nanometers, and the diameter of the
silicon nanocrystal is between 4 and 8 nanometers.