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 hydride vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor deposition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a network of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution result in essentially different surface morphologies, respectively: (i) low-angle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislocations. The Si doping of the GaN templates was found to enhance defect interaction in the templates and to enable a reduction of the dislocation density in the overgrown thick GaN films, although it does not lead to an improvement of the overall structural properties of the material.