GROWTH AND ENERGETICS OF GA AND AL CHAINS ON SI(112)

We present a low-energy electron diffraction and Auger electron spectr oscopy (AES) study of the growth of Al and Ga chains on Si(112) substr ates. For substrate temperatures between 500 and 650-degrees-C growth proceeds first by the creation of metal atom chains along the step edg es of the (112) surface. Once the step-edge sites have been occupied, a state defined here as ''saturation coverage,'' excess deposition lea ds to island formation with no further increase in the metal AES signa l intensity. The clean Si(112) (1 X 2) surface reconstruction is remov ed upon the formation of the metal chains so that the equivalence of a djacent single-layer-height steps is restored. At the saturation cover age both the Al and Ga chains exhibit a sixfold periodicity along the step edge, or [110BAR], direction. Below the saturation coverage these chains can also exhibit a fivefold periodicity along the same directi on. We propose a model in which the periodicities of the chains are de termined by the density of dimerized Si edge atoms, i.e, metal atom va cancies, whose presence balances the tensile stress imposed by the lar ger metal atoms. We investigate the relative binding energies of Al an d Ga to the step-edge sites and find that Al atoms are more strongly b ound. At substrate temperatures near 600-degrees-C die deposition of A l on a Ga saturated surface leads to the complete substitution of Ga b y Al atoms at the step-edge sites.