Effect of Si doping of metalorganic chemical vapor deposition-GaN templates on the defect arrangement in hydride vapor phase epitaxy-GaN overgrown layers

Two different types of dislocation arrangements have been observed in hydri de vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor dep osition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a netw ork of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution re sult in essentially different surface morphologies, respectively: (i) low-a ngle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislo cations. The Si doping of the GaN templates was found to enhance defect int eraction in the templates and to enable a reduction of the dislocation dens ity in the overgrown thick GaN films, although it does not lead to an impro vement of the overall structural properties of the material. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)08422-X].