EFFECT OF SURFACE POLARITY ON GALLIUM ADSORPTION ON 6H-SIC(0001) SURFACES - AN STM STUDY

We have performed the first STM study of gallium adsorption on both th e Si and C terminated 6H-SiC(0001) surfaces. The development of surfac e structures was followed as a function Ga coverage. On both the Si-te rminated root 3 x root 3 and C-terminated 2 root 3 x 2 root 3 surfaces , coverages of less than 1/2 ML resulted in a disordered phase. Increa sing the coverage to greater than 1/2, but less than 1 ML produced ord ered phases. On the Si-terminated side this consisted of parallel rows of Ga atoms arranged in three different domains, oriented at angles o f 120 degrees with respect to each other. Thus the surface symmetry wa s reduced from three-fold to two-fold. On the C-terminated side, it co nsisted of interlocking rings of 12 atoms, which appear alternately br ight and dark in the STM image. Thus the original threefold symmetry o f the SIC surface was preserved. On both surfaces, full monolayer cove rage led to the formation of the (1x1)Ga structure.