Elastic softening of sapphire by Si diffusion for dislocation-free GaN

Here we report the formation of dislocation-free GaN deposited on a sapphire substrate with an Si-diffused surface layer on top. As is widely accepted, sapphire is elastically harder than GaN. Geometric phase analysis, a strain mapping technique that is used with a transmission electron microscope, shows that, if a small amount of Si is incorporated into sapphire, it becomes elastically softer than GaN. We suggest that the elastically soft sapphire surface layer can accommodate the large mismatches at the GaN/sapphire interface, which necessarily produces dislocation-free GaN.