Graphene-assisted spontaneous relaxation towards dislocation-free heteroepitaxy

Although conventional homoepitaxy forms high-quality epitaxial layers1–5, the limited set of material systems for commercially available wafers restricts the range of materials that can be grown homoepitaxially. At the same time, conventional heteroepitaxy of lattice-mismatched systems produces dislocations above a critical strain energy to release the accumulated strain energy as the film thickness increases. The formation of dislocations, which severely degrade electronic/photonic device performances6–8, is fundamentally unavoidable in highly lattice-mismatched epitaxy9–11. Here, we introduce a unique mechanism of relaxing misfit strain in heteroepitaxial films that can enable effective lattice engineering. We have observed that heteroepitaxy on graphene-coated substrates allows for spontaneous relaxation of misfit strain owing to the slippery graphene surface while achieving single-crystalline films by reading the atomic potential from the substrate. This spontaneous relaxation technique could transform the monolithic integration of largely lattice-mismatched systems by covering a wide range of the misfit spectrum to enhance and broaden the functionality of semiconductor devices for advanced electronics and photonics. The spontaneous relaxation of misfit strain achieved on graphene-coated substrates enables the growth of heteroepitaxial single-crystalline films with reduced dislocation density.