Reflectance anisotropy spectroscopy (RAS) has been employed to characterize the overlayer growth of GaAs onto sub to one monolayer coverages of Si delta layers deposited on the GaAs(001)-c(4x4) surface. The low growth temperature (400 degrees C), required to avoid spreading of the dopant away from the delta plane, has meant that the study of a RAS feature related to the linear electro-optic (LEG) effect is complicated by disordering at the GaAs surface. This disordering is induced not only by the growth temperature, but also by the presence of the Si delta layer itself. Variable thickness studies indicate that the LEG-induced signal is dependent on the held profile in the surface layer. It has been observed that the intensity of the LEG feature, as a function of Si coverage, reaches a maximum at similar to 0.01 ML (similar to 6.3x10(12) atoms cm(-2)) in agreement with previous studies of the site occupancy of Si delta layers.