Mechanism of large area dislocation defect reduction in GaN layers on AlN∕Si (111) by substrate engineering

A reduction of edge dislocations in the GaN layer on Si substrate by almost an order of magnitude to 8.0×107∕cm2 and reduction in screw dislocations by a factor greater than 4 are achieved for the film grown on the Si (111) substrate engineered to have a polycrystalline defective layer at the AlN∕Si interface. The formation of a polycrystalline defective layer at the AlN∕Si interface by N+ ion implantation provides substrate conditions that result in a heteroepitaxial GaN film with much improved surface morphology and better crystal quality as compared to the film grown directly on AlN∕Si. A mechanism of dislocation defect reduction in the epitaxial film is given based on the detailed study of AlN∕Si interfaces as well as the evolution of the AlN buffer layer in the context of this substrate engineering technique, which shows partial decoupling of the III-nitride layers from the substrate to be responsible for the improved characteristics.