R. Galloni

Optical, structural and electrical properties of device-quality hydrogenated amorphous silicon-nitrogen films deposited by plasma-enhanced chemical vapour deposition

Abstract High-electronic quality hydrogenated amorphous silicon-nitrogen (a-Si1-xNx: H) films with an energy gap in the range 1.9-2.7eV have been deposited by plasma-enhanced chemical vapour deposition in silane-ammonia gas mixtures at two different gas residence times and in hydrogen-diluted silane-ammonia gas mixtures. Compositional, structural, electrical and optical properties have been investigated. For the first time the effects of hydrogen dilution of SiH4 + NH3 gas mixtures on the a-Si1-xNx: H network is reported. We have observed that hydrogen dilution decreases hydrogen incorporation and increases nitrogen incorporation, promoting a higher connectivity of the a-Si1-xNx :H network. All films show good electronic properties, comparable with or superior to those of amorphous silicon-carbon films, which are improved in films deposited from hydrogen-diluted gas mixtures.

Photoluminescence and electroluminescence properties of a-Si1−xNx:H based superlattice structures

A strong increase in the room temperature photoluminescence efficiency in a-Si 1-x N x :H multilayer structures with respect to thick single well layers is reported. This result has been correlated to carrier confinement in the well layers. The multilayer structures consist of a periodic sequence of barrier (E 04 = 5.0 eV or 4.2 eV) and well layers (E 04 = 2.1 to 2.6 eV), deposited by plasma enhanced chemical vapor deposition. Optical properties of these structures show a blue shift of the absorption edge, and evidence that the defect density associated with the internal interfaces is negligible. Electroluminescent devices have been obtained by inserting an a-Si 1-x N x :H multilayer in a p-i-n structure. Such devices show a broad electroluminescence peak, in the yellow region of the visible spectrum, at about 2.1 eV.