Effect of surface polarity on gallium adsorption on 6H-SiC surfaces

We have performed the first scanning tunneling microscopy (STM) study of gallium adsorption on both the Si-terminated 6H-SiC(0001) (√3 × √3) and C-terminated 6H-SiC(0001) (2√2 × 2√3) surfaces. The structure of the Ga terminated 6H-SiC surface showed strong polarity dependence. On the Si-terminated √3 × √3 surface, parallel rows of Ga atoms arranged in three different domains oriented at 120° with respect to each other at 1 ML coverage were observed. On the C-terminated 2√3 × 2√3 surface, sets of two concentric rings formed an overall 4√3 × 4√3 reconstruction at 1 ML coverage. We propose a structural model for the 4√3 × 4√3 structure which explains the STM image.