The effect of a Ga prelayer on the beginning of GaAs epitaxy on Si

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Abstract
The formation of GaAs islands is a major effect at the beginning of GaAs-on-Si epitaxy. The density of nucleation sites for the islands and the manner of their subsequent coalescence will influence the dislocation density of the final GaAs film. In this paper the effect on GaAs-on-Si epitaxy of a Ga-prelayer treatment is studied with photoemission core level spectroscopy and high resolution transmission microscopy (HTEM). Experiments are carried out with GaAs film thicknesses in the range from one monolayer to around 50 nm. Core level spectroscopy results for the monolayer films give information about the bonding character at the interface and suggest methods of improving the degree of two-dimensional growth. A particular Ga-prelayer technique is examined with HTEM using a wedge-shaped GaAs-on-Si sample. This allows side-by-side comparisons of areas with and without the Ga prelayer as a function of GaAs thickness. At thicknesses of around 5 nm, it is shown that the Ga prelayer yields islands with a lower wetting angle than those obtained with no prelayer. The Ga-prelayer technique also gives better surface morphology at thicknesses of around 50 nm.