Two different types of dislocation arrangement were observed in hydride vapour-phase epitaxial GaN films which had been grown onto sapphire substrates by using undoped or Si-doped GaN templates that had been grown via metal-organic chemical vapour deposition. One type comprised mainly straight threading dislocations that were parallel to the [00•1] direction in layers grown onto an undoped template. The other type comprised a network of interacting dislocations (edge, screw, mixed) in layers grown onto a Si-doped template. The 2 types of defect distribution resulted in essentially different surface morphologies. The first type led to low-angle grain boundaries that were formed from pure edge dislocations around spiral grown hillocks. The second type led to smooth surfaces which were intersected by randomly distributed dislocations. The Si-doping of GaN templates was found to enhance defect interaction within them, and permit a reduction of the dislocation density in the overgrown thick GaN films. However, this did not lead to an improvement in the overall structural properties.

Effect of Si Doping of Metalorganic Chemical Vapour Deposition-GaN Templates on the Defect Arrangement in Hydride Vapour Phase Epitaxy-GaN Overgrown Layers. T.Paskova, E.Valcheva, J.Birch, S.Tungasmita, P.O.A.Persson, R.Beccard, M.Heuken, B.Monemar: Journal of Applied Physics, 2000, 88[10], 5729-32