Influence of high-temperature annealing on the properties of Fe doped semi-insulating GaN structures

The properties of semi-insulating GaN films doped with Fe were studied after rapid thermal annealing (RTA) at temperatures 750-1050 degreesC and furnace annealing in hydrogen at temperatures up to 850 degreesC. It was shown that the Fe in such samples is distributed nonuniformly, showing a clear minimum near 0.5-1 mum from the surface. The Fe concentration increases toward both interfaces. The Fermi level in the as-grown state is pinned by deep levels near E-c-0.5 eV whose concentration is similar to3x10(16) cm(-3). The room temperature resistivity is on the order of 2x10(10) Omega/square. RTA at temperatures higher than 850 degreesC leads to increasing roughness of the surface and decreases of the sheet resistivity and the cathodoluminescence intensity. The density of deep traps also greatly decreases. The results are explained by partial evaporation of nitrogen from the surface upon annealing. The effect becomes much more pronounced for furnace annealing in hydrogen for times on the order of 15 min and in fact the annealing temperature of 850 degreesC seems to be the highest practicable under these conditions without destroying the surface morphology. (C) 2004 American Institute of Physics.