MULTIORIENTATIONAL GROWTH OF AL ON GAAS(001) STUDIED WITH SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy has been used to study the initial stage s of Al growth on decapped (2 X 4)/c(2 X 8) GaAs(001). Three orientati ons have been observed for the clusters of Al that form. On nominally flat GaAs(001) surfaces, Al(001)- and Al(O11)-oriented clusters are do minant. These two types of clusters nucleate with the same probabiliti es for Al depositions at 60, 200, and 300 degrees C, indicating the im portance of the intrinsic properties of the growth system rather than temperature in determining the Al crystal orientation. A model that co nsiders energy arguments is used to rationalize the observed populatio n of Al orientations. In contrast, Al(011)- and Al(011)R-oriented clus ters dominate for growth on stepped GaAs(001), an effect related to an increase in the interface free energy for Al(001)-oriented clusters a t steps. Previous results of this growth system are discussed in the c ontext of this model.