Properties and annealing stability of Fe doped semi‐insulating GaN structures

The properties of semi-insulating GaN films doped with Fe are reported. The 300 K sheet resistivity of the films is 2 × 1010 Ω/square with an activation energy of the dark conductivity of 0.5 eV. The Fermi level is also pinned at EC–0.5 eV. The concentration of the 0.5 eV traps in the Fe doped portion of the films was 3 × 1016 cm–3. Also present is a high concentration of deeper electron traps with the level near EC–0.9 eV and of hole traps with level near EV+0.9 eV. Intra-center transitions of the Fe3+ center are observed in the photoluminescence spectra. The stability of the films were studied after rapid thermal annealing (RTA) at temperatures 750–1050 °C and furnace annealing in hydrogen at temperatures up to 850 °C. The Fe is distributed nonuniformly, with a minimum near 0.5–1 µm from the surface. RTA at 850 °C leads to roughness of the surface and decreases of the sheet resistivity and the cathodoluminescence intensity. The density of deep traps also greatly decreases. The effect becomes much more pronounced for furnace annealing in hydrogen for times on the order of 15 minutes and 850 °C is the highest practicable under these conditions without destroying the surface morphology. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)