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(11 (2) over bar0) from the AlN underlayer are inclined away from the [0001] axis toward the (1 (1) over bar 00) 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(11 (2) over bar3) glide on (0 (1) over bar 11) planes when they enter the AlGaN film to generate interfacial misfit dislocations lying along the ((2) over bar 110) directions at the AlGaN/AlN interface. (C) 2010 The Japan Society of Applied Physics