Nanoscale Study of the Hydrogenated Amorphous Silicon Surface

Abstract

ABSTRACTA scanning tunneling microscope has been used to study the topology of the surface of device-quality, hydrogenated Amorphous silicon deposited by rf discharge from silane or “hot wire” CVD. The substrates were oxide-free single-crystal silicon or GaAs. Films studied were either grown in our laboratory and observed with no air exposure, or grown at other laboratories producing device-quality photovoltaic cells and viewed after air exposures of less than 30 Minutes. Thin films (10 nm) representing early growth stages appear significantly smoother than the thicker films. The topology of thick films (> 50 nm) has large variations over individual samples. While many regions can be characterized as “rolling hills”, atomically flat areas are sometimes observed nearby in our films. In most regions the observed slopes were 10% or less from the horizontal, but some steep-sided valleys, indicating incipient voids, are seen. Overall surface roughness measured on sub-Micron areas of our films is very inhomogeneous. Uniformity of the films grown off site was much better, although no atomically flat regions were observed, surface roughness can be estimated.