AES and LEED Studies Correlating Desorption Energies With Surface Structures and Coverages for Gallium on Si(100)

Gallium interactions with Si(100) are studied with Auger electron spectroscopy and LEED to correlate the desorption energies with surface coverages and structures in isothermal desorption experiments. Some evidence for a temperature-induced change from a Stranski--Krastanov to a Volmer--Weber growth mode between 600 and 700K is presented. In the temperature range 800-900K, three different kinetic regimes are observed. Between 0 and 0.5 monolayers (ML), first-order desorption is observed from a well-ordered Ga overlayer (Si:Ga 2 x 2), with a desorption energy of 2.9 plus/minus 0.2 eV and a pre-exponential factor of 3 x 10 exp 16 plus/minus 1 s exp --1 . Between 0.5 and 1 ML, first-order desorption is also observed from a well-ordered Ga layer (Si:Ga 8 x 1), but the desorption energy decreases to 2.3 plus/minus 0.2 eV with a pre-exponential factor of to 8 x 10 exp 12 plus/minus 1.2 s exp --1 . Above 1 ML, zeroth-order desorption from Ga islands on top of an ordered Ga monolayer is observed, and the desorption energy of the combination of surface species is 2.61 plus/minus 0.07 eV with a pre-exponential factor equal to (4 plus/minus 3) x 10 exp 13 ML s exp --1 . It is suggested that atoms from the islands and the ordered layer are kinetically coupled, and that the islands cover too little of the surface to exhibit the bulk heat of vaporization of liquid Ga 2.8 eV. The observed kinetic regimes are correlated with the surface structures proposed in the preceding paper. 12 ref.--AA