On the growth of silver on GaAs{001} surfaces

Abstract

A study of the epitaxial growth of Ag on GaAs{001} layers prepared by molecular beam epitaxy (MBE) is reported. Different experimental approaches were used in order to provide various experimental results on the main metallurgical aspects of this type of growth which are interface related: epitaxial relationships, mode of growth and interfacial diffusion. Epitaxial relationships were studied by LEED. Two main orientations of the metal overlayer were found depending on the growth temperature: below 200°C Ag is oriented (001) while above this temperature the orientation becomes (001). The mode of growth was studied by the classical Auger signal-time method and also by less conventional approaches using Auger line shape variation during the first stages of the growth and electron loss spectroscopy. Direct observation of the layer topology was provided by scanning electron microscopy. From the over all experimental data the following general conclusions have been drawn: (i) For high deposition rate and low temperature, the Ag growth is very close to the ideal two-dimensional layer-by-layer mode. (ii) Deviations from the layer-by-layer mode are observed when the growth temperature increases or when the growth rate decreases. This effect of the growth rate is closely associated with adsorption from the residual gas phase. A study of interfacial diffusion by AES has shown that metallic Ga outdiffuses from the GaAs substrate at elevated temperature and segregates at the surface of the Ag layer.