Epitaxy of Germanium on SI(001) Grating Templates

Abstract

Epitaxial Ge films (< 3 ML) have been grown at elevated temperatures on Si(001) grating substrates (repeat spacing of 2.0 µm) and imaged using room temperature scanning tunneling microscopy (STM). The Ge films exhibit the 2xn reconstruction associated with missing dimer rows. The value of n and the growth morphology are influenced by the deposition rate and by annealing. At substrate temperatures of 600° C and deposition rates >0.5 ML/min., islands elongated along the the dimer row direction nucleate at steps and on terraces. With sufficient annealing at 800° C, the islands coarsen and are eventually eliminated. The roughness of the Atype step becomes greater than that of the B-type step, which is the reverse of the situation with pure Si(001). The separation between missing dimer rows and hence the value of n are increased by annealing. Differences in substrate terrace widths due to the periodically varying step density of the gratings affect the growth modes: two-dimensional islands occur near the extrema of the gratings whereas step flow occurs when steps are separated by ~ 150 Å or less.