Low-temperature Ge heteroepitaxy on GaAs(001)

Abstract

It is shown through the use of low-energy electron diffraction and high-energy x-ray photoelectron diffraction that very nearly layer-by-layer epitaxial growth of ultrathin Ge films can be achieved on GaAs(001). Superior overlayer uniformity has been attained by minimizing the surface defect density on the substrate and growing at a low enough substrate temperature to prevent high rates of surface diffusion and the resulting agglomeration of adatoms. When these two conditions are achieved, clustering is minimized during the initial stages of epitaxy. We have found that the first monolayer of Ge intermixes with the substrate to a limited extent when grown at 220 °C. Partial third-layer formation occurs as a result of the deposition of two monolayer equivalents (ML eq), and some fifth-layer formation occurs during the deposition of the fourth ML eq, but is limited in extent. These films exhibit less clustering but are also not as well ordered as those grown at 320 °C.