RECENT UNDERSTANDING OF THE GROWTH-PROCESS OF AMORPHOUS-SILICON FROM A SILANE GLOW-DISCHARGE PLASMA

The film growth process of hydrogenated amorphous silicon (a-Si:H) fro m a monosilane glow-discharge plasma as been investigated as a represe ntative case of thin him growth from a glow-discharge plasma. On the b asis of our understanding of the gas phase as well as surface-reaction processes obtained from the results of a variety of process diagnoses such as infrared laser-absorption spectroscopy and infrared reflectio n-absorption spectroscopy, a reaction model explaining the determinati on step of defect density in the resulting a-Si:H has been proposed. T he defect (dangling bond) density of a-Si:H has been controlled throug h the surface-diffusion length of silyl radicals produced in the monos ilane plasma. This allows us to obtain low defect density a-Si:H havin g a range of optical band gaps and to avoid the use of alloying with e lements other than hydrogen. At high temperature, precursor assisted d efect suppression (PADS) produces a low band gap and defect density. A t low temperature, heating of precursors in the gas phase allows defec t reduction by energized precursors (DREP) to attain lower defect dens ity. Furthermore, the electron and hole mobilities in the resulting a- Si:H have been controlled by making use of the kinetic energy of ionic species impinging on the film-growing surface from the plasma.