The nucleation mechanism and crystalline perfection of InAs on Si(100) were found to depend strongly on the substrate bias voltage Vs used to accelerate Ar ions to the growing film during triode ion‐assisted deposition. Increasing the Vs value used during the first ∼10 monolayers (ML) of growth from 15 to 30 V decreased the x‐ray diffraction rocking curve full width at half maximum (FWHM) by a factor of ∼2. Further increases in Vs yielded an increase in the FWHM. Reflection high‐energy electron diffraction studies showed that the use of Vs=30 V promoted layer‐by‐layer nucleation. While three‐dimensional islands formed at a critical coverage θcr of 2 – 3 ML for Vs=15 V, increasing Vs to 30 V increased θcr to ∼10 ML. The fact that Vs=30 V both promoted layer‐by‐layer growth and decreased the FWHM suggests that defect generation is dependent upon the nucleation mechanism.