REAL-SPACE INVESTIGATION OF INITIAL GROWTH-PROCESS OF HYDROGENATED AMORPHOUS-SILICON ON A GRAPHITE SUBSTRATE

Initial growth of hydrogenated amorphous silicon (a-Si:H) from silane plasma on a cleaved surface of highly oriented pyrolytic graphite (HOP G) has been investigated by means of in situ x-ray photoelectron spect roscopy (XPS) and atomic force microscopy (AFM). At a substrate temper ature of 110 degrees C, island nuclei were formed on atomically flat t erraces as well as along the steps of the HOPG surface. At an increase d substrate temperature of 230 degrees C, the nucleation occurred only along the steps. Hydrogen plasma treatment of the HOPG surface prior to the a-Si:H deposition drastically changed the growth mode to a homo geneous coverage of the surface from the beginning of film deposition at both temperatures. In order to understand and analyze these results , we propose a mechanism, from analogy to epitaxial film growth, that consists of the adsorption, migration, and fixation (pinning) of precu rsors on the surface and of subsequent nucleation and growth of film.