The Atomic Nature of OMVPE Growth.

In situ x-ray scattering has been used to study the nature of a growing film (ZnSe on GaAs) during organometallic vapor phase epitaxy. This first in situ study of non-UHV growth revealed a surprisingly stable and well-ordered p(2x1) reconstruction of the growing ZnSe surface despite the presence of organic reaction by-products and a near-atmospheric pressure of hydrogen carrier gas. The p(2x1) reconstruction results from the dimerization of the selenium terminated surface and from additional subsurface distortions. Lineshape analysis indicates that the initial film is a two dimensional, strained layer and that, as growth continues, the film evolves to yield diffraction peaks characteristic of a free standing bulk film. Investigating transient kinetic effects during alternate source epitaxy, dramatic changes in the specular x-ray reflectivity were found as organometallic sources are alternated. These changes are explained by cyclic smoothing and roughening of the surface, or, alternatively, by saturation of the surface with partially decomposed diethylselenium. The response of the specular reflectivity (tau ~40 sec) to changes in the gas composition (tau ~1 sec) is kinetically limited, probably by surface reactions. These results demonstrate the power of in situ x-ray scattering studies in the characterization and deciphering of these complex processes. We expect that further application will result in a deeper understanding of non-UHV growth and subsequent improvements in the optical, electronic and structural properties of atomically engineered thin films.