Superlattices and multilayers in hydrogenated amorphous-silicon devices

An investigation of the physical properties of ultrathin multilayer structures that consist of hydrogenated amorphous silicon (a-Si:H) and silicon-based compounds such as a-Si_1-xN_x :H and a-Si_1-xC_x:H prepared by either plasma chemical vapor deposition (CVD) or direct photo-CVD is discussed. X-ray interference in the multilayers shows that the heterojunction interface is atomically flat and abrupt. The band offset is successfully determined by X-ray photoelectron spectroscopy. The energy band profile in the superlattices can therefore be designed. The carrier confinement in the ultrathin a-Si:H layers causes a blue shift of the optical bandgap and luminescence spectrum due to the quantization effects. Better understanding of the quantum size effects in the multilayers permits the introduction of superlattice structures to devices such as solar cells, thin-film transistors, and light-emitting diodes. Some of the experimental results are discussed