Thick c-plane unintentional doped and iron-doped GaN substrates were grown by hydride vapor phase epitaxial technique on sapphire Substrates. The morphology and crystalline quality of the freestanding samples show no evident degradation due to iron doping. Low-temperature photoluminescence measurements show reduction of the exciton-bound to neutral impurities band intensities with iron doping increase. Near-infrared photoluminescence studies confirm the incorporation and activation of iron impurities. Variable temperature resistivity measurements verified that the iron-doped films are semi-insulating. (c) 2008 Elsevier B.V. All rights reserved.