Graphene-assisted spontaneous relaxation towards dislocation-free heteroepitaxy

Although conventional homoepitaxy forms high-quality epitaxial layers(1-5), 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 performances(6-8), is fundamentally unavoidable in highly lattice-mismatched epitaxy(9-11). 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.