Real-time synchrotron x-ray studies of III-V nitride growth

My thesis research has examined the atomic structure and surface morphology of the group III-nitrides and related thin films during growth using real-time synchrotron-based x-ray scattering and lab-based x-ray diffraction. The synchrotron-based surface-sensitive x-ray techniques monitor the surface evolution in real time without interruption of the process due to the non-invasive nature of x-rays. By utilizing the high brilliance of synchrotron radiation, x-ray measurements can overcome a number of the difficulties encountered in traditional electron-based and scanning techniques, providing important complementary information on surface topography evolution, film nucleation and strain relaxation.; A unique ultra-high vacuum growth chamber for these experiments was designed and constructed by our group. I have set up and optimized the system for thin film growth by molecular beam epitaxy. The real-time x-ray studies facility consists of a base diffractometer and an ultra-high vacuum chamber with processing and analysis instrumentation.; Understanding how heteroepitaxial thin film nucleation and initial growth occurs in the presence of mismatch strain is an issue of widespread significance in materials physics. My thesis presents detailed studies of the plasma nitridation of c-plane sapphire at low and high substrate temperatures, which converts the sapphire surface to relaxed AIN. Models of the film nucleation and growth were developed to explain the experimental results.; Surface morphology evolution during continued thin film growth is a complex issue, involving stochastic deposition kinetics and surface diffusion. My thesis research has studied the surface morphology evolution during GaN growth by migration-enhanced molecular beam epitaxy which utilizes alternative supplies of Ga and N sources to achieve atomic flat surface and large area uniformity. Subsequent formation of self-organized GaN nanodots by droplet heteroepitaxy and plasma nitridation has also been studied, as has the kinetics of Ga nanodroplet formation and evaporation on substrate surfaces.; Finally I have investigated ordering in group III-nitride films, a complex phenomenon believed to be driven by processes at the growing surface, possibly influenced by strain. My thesis describes our observation of a new incommensurate ordering along the [0001] direction in wurtzite Al0.72Ga0.28 N alloys grown by plasma-assisted molecular beam epitaxy on c-plane sapphire.