But it is prone to degradation. Some of the varieties of amorphous silicon are amorphous silicon carbide (a-SiC), amor- phous silicon germanium (a-SiGe), microcrystalline silicon (c-Si), and amorphous silicon-nitride (a-SiN). Gallium arsenide (GaAs), copper, cadmium telluride (CdTe), indium diselenide (CuInSe2) and titanium dioxide (TiO2) are also materials that have been mostly used for thin-film PV cells.