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The time evolution of B diffusion and electrical activation after ion implantation and annealing at 800 and 900 °C is studied using secondary-ion mass spectrometry and spreading-resistance profiling. The time evolution at 800 °C is observed in both crystalline and post-amorphized samples. Amorphized samples show near-normal concentration enhanced diffusion. Crystalline samples show anomalous transient diffusion, with a rapidly diffusing low-concentration region and a static peak region above a critical concentration Cenh=3.5×1018 cm−3. The peak region above Cenh is shown to be electrically inactive. The static, inactive B is released over a period of many hours, compared with the transient diffusion enhancement which relaxes to near-normal within 30 min. The time evolution of B diffusion at 900 °C is observed as a function of implantation dose. A critical concentration for transient diffusion, Cenh=8×1018 cm−2, independent of dose, is observed at this temperature. The transient diffusion enhancement in the diffusing part of the B profile increases with dose, up to a dose of ∼5×1014 cm−3, and saturates at higher doses. A comparison with published data shows that Cenh∼ni within a factor 2 over the temperature range 550–900 °C. We interpret our observations in terms of a nonequilibrium point-defect model of diffusion and intermediate defect formation.

We report a study of iron doped GaN layers grown on sapphire and SiC by Metal Organic Chemical Vapor Deposition (MOCVD) using ferrocene as the Fe precursor. The influence of iron doping on the electrical, structural and morphological properties of the GaN layers was studied. A resistivity of 6x10 3 Ωcm and higher was achieved in contrast to 3 Ωcm for the undoped film. Defect selective etching showed that Fe doping increases the threading dislocation (TD) density which might be responsible for the increase in resistivity. A turn-on, turn-off effect is described and a memory effect which is responsible for a decrease of the surface quality of the samples. In situ annealing of the susceptor and the use of a clean liner after each growth run helps to reduce this effect and maintain the good quality of GaN layers.