Strain Relaxation Mechanisms in AlGaN Epitaxy on AlN Templates

Two strain relaxation processes have been observed in AGaN layers grown on thick AlN templates. In Process I, a-type threading dislocations (TDs) with b= 1/3 from the AlN underlayer are inclined away from the [0001] axis toward the directions when they enter the AlGaN film, forming dislocation line projection perpendicular to the Burger vector. In Process II, a+c-type TDs from the AlN underlayer with Burgers vector of b= 1/3 glide on {0111} planes when they enter the AlGaN film to generate interfacial misfit dislocations lying along the directions at the AlGaN/AlN interface.