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

Abstract

The properties of semi-insulating GaN films doped with Fe were studied after rapid thermal annealing (RTA) at temperatures 750–1050 °C and furnace annealing in hydrogen at temperatures up to 850 °C. It was shown that the Fe in such samples is distributed nonuniformly, showing a clear minimum near 0.5–1 μm from the surface. The Fe concentration increases toward both interfaces. The Fermi level in the as-grown state is pinned by deep levels near Ec–0.5 eV whose concentration is ∼3×1016 cm−3. The room temperature resistivity is on the order of 2×1010 Ω/square. RTA at temperatures higher than 850 °C 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 °C seems to be the highest practicable under these conditions without destroying the surface morphology.