Control of Medium Range Order in Amorphous Silicon via Ion and Neutral Bombardment

Abstract

ABSTRACTWe have observed the existence of medium range order via fluctuation microscopy in amorphous silicon grown at 230°C. We hypothesize that this structure develops during the highly non-equilibrium growth process; high densities of ordered surface nuclei are produced which are subsequently buried and forced into an unfavorable energy state. These nm sized regions are distorted in the bulk due to strain, but remain topologically crystalline. In this work, we alter the growth energetics both at the surface and sub-surface during magnetron sputter film deposition with two kinds of particle bombardment, respectively: a controllable flux of low-energy (20eV) Ar+ ions, and higher energy (100eV) D vs. H neutrals. With this method, we demonstrate for the first time control over the intensity of this medium-range structural order at a constant substrate temperature as seen primarily with fluctuation electron microscopy, but also Raman scattering, spectroscopic ellipsometry, and SAXS. We suggest that these bombardments can increase adspecie surface mobility or drive local sub-surface restructuring (“kinetic annealing”), thus increasing or decreasing the size, density and/or strength of the ordered regions.