HETEROEPITAXY, POLYMORPHISM, AND FAULTING IN GAN THIN-FILMS ON SILICON AND SAPPHIRE SUBSTRATES

The structure of GaN films grown by electron-cyclotron-resonance-assisted molecular beam epitaxy on Si(111), Si(001), basal-plane sapphire, a-plane sapphire, and r-plane sapphire substrates was studied with four-circle x-ray diffractometry. Phase content, domain size, inhomogeneous strain, and in-plane and out-of-plane domain misorientations were measured and compared for films grown on each type of substrate. Wurtzite and zinc blende polymorphs were found to coexist in films grown on Si(111). The two structures grow in the (0002) and (111) orientations, respectively, so that they may transform into each other via stacking faults on close-packed planes. Smaller amounts of zinc blende material were also found in predominately (0002) wurtzitic films on a-plane sapphire and (1120BAR) wurtzitic films on r-plane sapphire.