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 amorphous silicon deposited by rf discharge from silane. The substrates were atomically flat, oxide-free, single-crystal silicon or gallium arsenide. No evidence for island formation or nanoscale irregularities was seen in studies of 100-angstrom-thick films on either silicon or gallium arsenide. The topography of 1000- and 4000-angstrom-thick films has much variation; many regions can be characterized as ''rolling hills,'' but atomically flat areas have also been observed nearby. Generally, it appears that surface diffusion plays a role in smoothing the film topography. In most regions, the observed slopes were 10% or less from horizontal, but some steep-sided valleys, indicating incipient voids, were observed. The effect of the finite size of the scanning tunneling microscope probe tip is considered, this has an effect on the observed images in some cases.