Low-pressure chemical vapor deposition of GaN epitaxial films

GaN films were grown epitaxially on sapphire and 6H-SiC substrates by low-pressure chemical vapor deposition (LPCVD) using gallium(III) chloride and ammonia as gallium and nitrogen precursor, respectively. The properties of these samples were examined by X-ray diffraction, Hall effect measurements, secondary-ion mass spectroscopy (SIMS) and photoluminescence (PL). All GaN layers exhibit high free carrier concentrations between n = 2 x 10 18 and 5 x 10 19 cm - 3 caused by unintentional n-type doping. We provide evidence that this high unintentionally doping is linked to the oxygen content in the films. The correlation between the optical properties with respect to position and line shape of the band-edge luminescence and the electrical properties. i.e. the free carrier concentration, is discussed.