Amorphous superlattice structure devices

Novel types of amorphous silicon (a-Si) p-n junction diodes, solar cells, and ultraviolet (UV) sensors have been developed using superlattice structure a-Si films. To improve interface properties, the photo-CVD (chemical-vapor deposition) method was used to fabricate a-Si superlattice structure films, instead of the conventional plasma-CVD method. The photoconductivity vertical to the interfaces of the superlattice structure film was one to two orders higher than that of conventional a-SiC alloy film in the wide optical bandgap region. A p-n junction diode with an undoped a-Si/boron-doped a-SiC superlattice structure film for its p-layer was fabricated. The photocurrent of the diode was five times as high as that of a diode with a conventional p-a-SiC/n-a-Si film. The a-Si/a-SiC superlattice was used for the p-layer of a p-i-n type a-Si solar cell, resulting in a great improvement in collection efficiency in the short wavelength region. An a-Si UV sensor using the superlattice structure p-layer as the window layer of a p-i-n type photosensor also showed improved performance over conventional design