A TEM Study of AlN–AlGaN–GaN Multilayer Buffer Structures on Silicon Substrates

Two buffer structures based on Al x Ga 1 – x N solutions with silicon doping and without it have been studied by transmission electron microscopy. The structures have been grown on silicon substrates with the (111) orientation by metalorganic vapor-phase epitaxy with consistently decreasing Al content. A significant threading dislocation density reduction in the region of intermediate layers has been found at a change in the Al content from 32 to 23%. Phase decay and the phenomenon of compositional self-modulation in the Al x Ga 1 – x N layers in the direction of growth have been detected at an Al content equal to 32, 23, 12, and 4%. A model of the structure of layers in the region of composition modulation has been proposed.