AFM AND STM INVESTIGATIONS OF HYDROGENATED AMORPHOUS-SILICON - TOPOGRAPHY AND BARRIER HEIGHTS

As-grown films of hydrogenated amorphous silicon (a-Si:H, highly phosp horous-doped) were investigated by atomic force microscopy (AFM) and s canning tunneling mi microscopy (STM). Hills up to 10 nm in height and 10 to 20 nm in diameter have been observed by AFM. By using STM in a new high-sensitivity mode, (1) atomically smooth areas (rough ness abo ut 0.3 Angstrom rms) which occur at the top of the hills, (2) subnanom eter structures several Angstrom in height which cover large parts of the surface have been identified. Simultaneous measurements of the loc al apparent barrier heights (LABH) show a clear correlation to the top ography. Areas showing subnanometer structures have always low LABHs w hile the highest values of the LABH occur on the smooth areas.