Effects of substrate type on the characteristics of GaN epitaxial films grown by molecular beam epitaxy

Films of GaN have been grown simultaneously on three different substrates, sapphire, silicon carbide and GaN, by molecular beam epitaxy. The structural and optical properties of the films have been studied using x-ray diffraction techniques and low-temperature photoluminescence spectroscopy respectively. There is a clear correlation between the structural and optical properties of the film and the nature of substrate. The lattice parameter of the film is shown to depend on the type of substrate. The incorporation of shallow donors is also strongly influenced. The effect of lattice parameter, mismatch and differential thermal expansion on film properties is discussed.