Atomic scale studies of epitaxial growth processes using X-ray techniques

In this work we have applied grazing incidence X-ray scattering to the study of nucleation and growth of GaAs by organometallic vapor phase epitaxy. Using the sensitivity of scattering at the 110 crystal truncation rod (CTR) position to the smoothness of the surface, we are able to monitor the crossover from layer-by-layer to step-flow growth. More detailed information about the nucleation process was determined by using diffuse scattering near the CTR position to measure the spacing of two-dimensional islands during growth as a function of flux and deposition temperature. Application of standard nucleation theory to the analysis of this data suggests that the critical island size during OMVPE growth is likely to be much larger than a single adatom, in contrast with what is usually assumed for semiconductor systems.