Scanning tunneling microscopy study of rough Si films deposited on Si(1 1 1)

Series of silicon films were grown by thermal evaporation on Si(1 1 1) substrates at temperatures between ∼240°C and ∼500°C under ultrahigh-vacuum conditions, and examined with scanning tunneling microscopy. Two series of films grown at ∼240°C and ∼400°C showed a trend toward multilayer root-mean-squared (rms) roughness as thicknesses of tens to hundreds of bilayers were reached. The roughening of the ∼240°C deposition series appeared to slow as thicker films were deposited; the effective power law for the rms roughness suggested by measurement of the thinner films was t0.4±0.1, which is faster than that consistent with linear diffusion dynamics. The growth at ∼400°C appeared to be multilayer epitaxial and showed an increase in lateral feature size with deposition time. At higher deposition temperatures of ∼450°C and ∼500°C, a flatter terraced morphology with dotted depressions was seen. Some of these vacancies appeared in straight lines, usually running parallel to the rough steps, indicating a pinning effect on the growing film due to the initial substrate step morphology. The degree of pinning was analyzed in the framework of the directed-percolation depinning model. The roughening behavior exhibited by the films in this study results from a pinning effect and is attributed partially to the incorporation of carbon and oxygen in these films.