Structural study of GaN(As,P) layers grown on (0001) GaN by gas source molecular beam epitaxy

Transmission electron microscope (TEM) and transmission electron diffraction (TED) examination has been performed to investigate microstructural properties of gas source molecular beam epitaxial GaN(As,P) layers grown on (0001) GaN/sapphire at temperatures in the range 500 - 760 degrees C. As for the GaNAs, we report the observation of ordering with a space group P3m1 in the layer grown at 730 degrees C. The layers grown at temperatures below 600 degrees C are polycrystalline, whist the 730 degrees 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. As for the GaNP, it is shown that the layers grown at temperatures less than or equal to 600 degrees C experience phase separation resulting in a mixture of GaN-rich and GaP-rich GaNP with zinc-blende structure. However, the layers grown at temperatures greater than or equal to 730 degrees C are found to be binary zinc-blende GaN(P) single crystalline materials. The layers grown at temperatures greater than or equal to 730 degrees C consist of two types of micro-domains, i.e., GaN(P)(I) and GaN(P)(II); the former having twin relation to the latter.