Detailed study of effects of duration of pre-AlN-growth trimethylaluminum step on morphologies of GaN layers grown on silicon substrate by metal organic chemical vapor deposition

In this study, we investigate how the duration of trimethylaluminum (TMAl) flow steps used before aluminum nitride (AlN) growth affects the crystal quality of an AlN layer and, in turn, the surface morphologies of a gallium nitride (GaN) layer in a GaN-on-AlN-on-silicon (111) structure. A high pit density was observed on a GaN surface grown under an incorrect pre-AlN-growth TMAl step duration. Transmission electron microscopy revealed that crystallographically inclined AlN crystals were contained in the AlN layer grown after the duration, and that these crystals impeded the GaN layer from growing. When the pre-AlN-growth TMAl step duration was short, a high density of dislocations was generated in the AlN layer, and polycrystalline growth began on the AlN surface. When the duration was long, an excessive amount of aluminum reacted with silicon, forming a silicon-aluminum alloy, and the AlN layer grown on this alloy contained crystallographically inclined crystals.