We present a new method for growing heterostructures of semimetallic ErAs in GaAs that appears to avoid the formation of antiphase domains which have historically plagued the ErAs/GaAs material system. With traditional epitaxial growth, antiphase domains nucleate in the GaAs overgrowth of ErAs films, due to the mismatch in rotational symmetry between the rocksalt ErAs and zincblende GaAs. We leverage the recent discovery that, below a critical areal density during growth, surface erbium adatoms will preferentially incorporate into subsurface ErAs nanoparticles. As compared to traditional layered heterostructure growth, this method offers the advantage that a thin layer of GaAs floats on the surface and remains registered to the substrate, preventing antiphase domain formation during subsequent III-V growth. Samples were grown by solid-source molecular beam epitaxy in a Varian Gen II system. The growth method consisted of: (a) growth of an ErAs nanoparticle layer which was overgrown with GaAs. (b) The substrate was heated to 600˚C and an erbium flux was initiated; the erbium diffused through the GaAs capping layer to the underlying ErAs nanoparticles, displacing gallium and growing the ErAs into a full film. (c) The ErAs film continued to grow vertically through the GaAs cap layer, which was used to seed the subsequent growth of III-V layers, mitigating antiphase domain formation. To verify this growth mechanism, ErAs films were grown with varying GaAs cap thickness and characterized with in situ reflection high energy electron diffraction (RHEED) and ex situ transmission electron microscopy (TEM). Imaging was performed with a 200 kV FEI Tecnai TF20 instrument, equipped with a Schottky field emitter (zirconium oxide coated tungsten tip), and X-twin objective lens. TEM analysis was obtained with the sample aligned to the nearest <110> zone axis of the substrate. Spherical Aberration (Cs) free high angle annular dark (HAADF) field and bright field (BF) Scanning-TEM (STEM) images were acquired using a JEOL JEM-ARM200F attaining information transfer to <0.1nm. TEM images of ErAs films grown with conventional MBE are compared with ErAs films grown by nanoparticle-seeded growth. The conventionally grown films exhibited antiphase domains in TEM images and severely degraded RHEED during GaAs overgrowth. By contrast, the films grown by nanoparticle-seeded growth did not exhibit antiphase domains in the overgrown GaAs. These results demonstrate the ability to suppress antiphase domain formation by growing ErAs films through a GaAs cap that remains registered to the underlying substrate. We will discuss critical growth parameters, particularly the importance of the GaAs cap thickness, on the film and overgrowth quality. This provides a potential path towards epitaxial plasmonic devices containing multiple metallic layers.