Medium-Range Order in Amorphous Silicon Measured by Fluctuation Electron Microscopy. Final Report 23 June 1999-23 August 2002

摘要

Despite occasional experimental hints, medium range structural order in covalently bonded amorphous semiconductors had largely escaped detection until the advent of fluctuation electron microscopy (FEM) in 1996. Using FEM, we find that every sample of amorphous silicon and germanium we have investigated, regardless of deposition method or hydrogen content, is rich in medium range order. The paracrystalline structural model, which consists of small, topologically ordered grains in an amorphous matrix, is consistent with the FEM data; but due to strain effects, materials with a paracrystalline structure appear to be amorphous in diffraction measurements. We present measurements on hydrogenated amorphous silicon deposited by different methods, some of which are reported to have greater stability against the Staebler- Wronski effect.