Ordering and Microstructures of GaN_1-xAs_x Layers Grown on (0001) GaN/Sapphire Substrates

Transmission electron microscope and transmission electron diffraction examinations have been performed to investigate the ordering and microstructures of molecular beam epitaxial GaN_1-xAs_x layers grown on (0001) GaN/sapphire at temperatures between 500 and 730°C. We report the observation of ordering with a space group P3m1 in the GaNAs layer grown at 730°C. The GaNAs layers grown at temperatures below 600°C are polycrystalline, while the 730°C GaNAs layer has epitaxial relation to the GaN substrate. It is also shown that the GaNAs layers experience a structural change from a zinc blende phase to a wurtzite phase, as the growth temperature increases from 500 to 730°C.