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) (root 3 X root 3) and C-terminated 6H-SiC(<000(1)over bar>) (2 root 3 X 2 root 3) surfaces. The Structure of the Ga terminated 6H-SiC surface showed strong polarity dependence. On the Si-terminated root 3 X root 3 surfa ce, parallel rows of Ga atoms arranged in three different domains orie nted at 120 degrees with respect to each other at 1 ML coverage were o bserved. On the C-terminated 2 root 3 X 2 root 3 surface, sets of two concentric rings formed an overall 4 root 3 X 4 root 3 reconstruction at 1 ML coverage. We propose a structural model for the 4 root 3 X 4 r oot 3 structure which explains the STM image. (C) 1997 American Instit ute of Physics. [S0003-6951(97)00545-7].