Various heterostructures and methods of forming heterostructures are disclosed. A structure includes a substrate, a template layer, a barrier layer, and a device layer. The substrate comprises a first crystalline material. The template layer comprises a second crystalline material, and the second crystalline material is lattice mismatched to the first crystalline material. The template layer is over and adjoins the first crystalline material, and the template layer is at least partially disposed in an opening of a dielectric material. The barrier layer comprises a third crystalline material, and the third crystalline material is a binary III-V compound semiconductor. The barrier layer is over the template layer. The device layer comprises a fourth crystalline material, and the device layer is over the barrier layer.