NANOSCALE STUDY OF THE AS-GROWN HYDROGENATED AMORPHOUS-SILICON SURFACE

A scanning tunneling microscope has been used to study the topography of the as-grown surface of device-quality, intrinsic, hydrogenated amo rphous silicon deposited by rf discharge from silane. The substrates w ere atomically flat, oxide-free, single-crystal silicon or gallium ars enide. No evidence for island formation or nanoscale irregularities wa s seen in studies of 100-angstrom-thick films on either silicon or gal lium arsenide. The topography of 1000- and 4000-angstrom-thick films h as much variation; many regions can be characterized as ''rolling hill s,'' but atomically flat areas have also been observed nearby. General ly, it appears that surface diffusion plays a role in smoothing the fi lm topography. In most regions, the observed slopes were 10% or less f rom horizontal, but some steep-sided valleys, indicating incipient voi ds, were observed. The effect of the finite size of the scanning tunne ling microscope probe tip is considered, this has an effect on the obs erved images in some cases.