The solid-phase epitaxial growth of amorphized GaAs has been characterized to investigate the influence of both microscopic and macroscopic non-stoichiometry on the onset of twinning and subsequent interfacial non-planarity. Microscopic non-stoichiometry or equivalently, chemical disorder on an atomic scale, was produced by implanting samples with equal doses of both Ga and As ions. In such samples, the onset of twinning and interfacial non-planarity where independent of the energy deposited in vacancy production, the latter considered a first estimate of relative differences in microscopic non-stoichiometry between samples. Twinning and interfacial non-planarity are thus independent of microscopic non-stoichiometry or alternatively, microscopic non-stoichiometry may approach saturation over the given dose range. In contrast, macroscopic non-stoichiometry produced by implanting samples with Ga or As ions influenced both the onset of twinning and interfacial non-planarity. Excess Ga was observed to have a greater effect than excess As. The influence of a macroscopic non-stoichiometry may be indicative that the availabiltiy of a lattice constitutent and/or defect is rate-limiting during solid-phase epitaxial growth. Macroscopic non-stoichiometry may also yield preferrential nuclueation sites for twinning and in the presence of excess Ga, molten precipitates could contribute to an observed rapid amorphous-to-crystalline transformation.