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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.

We report a comparative investigation of MOCVD grown GaN epilayers deposited on misoriented 4H-SiC substrates. Crack-free layers can be grown on exact oriented substrates in contrast to growth on misoriented ones. Dependent on the degree of misorientation the crack patterns differ in density, distribution and orientation. The surface morphology and structural quality of GaN layers depend strongly on the substrate misorientation of the SiC substrate and very smooth layers with good structural quality and electrical properties were obtained for on-axis SiC.

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Al Ga N ∕ Ga N transistor heterostructures, caped by ∼2nm GaN layer, were investigated by contactless electroreflectance (CER) spectroscopy at room temperature. Below the AlGaN-related transition CER spectra have shown a clear resonance at the energy of ∼3.7eV, i.e., at much higher energy than the GaN band gap energy. The observed feature has been connected with the optical transition within the GaN cap layer. It was concluded that a surface GaN quantum well has been created by the deposition of nominally undoped (or Si-doped) GaN cap layer on AlGaN∕GaN transistor heterostructures.