Investigation of Mn incorporation on GaN(0001) by spin-polarized STM

We investigate the Mn substitution of Ga on GaN(0001) by spin-polarized scanning tunneling microscopy (SP-STM) using a Fe coated W tip. The GaN films are grown by plasma-assisted MBE on 6H-SiC(0001), with a metallic pseudo-1x1 (denoted ``1x1'') surface, consists of 2.3 ML Ga on top of the Ga-terminated GaN. Mn deposition on this surface results in the formation of domains of 5x5 and $5\sqrt 3 \times 5\sqrt 3 $ structures. First principles calculations show that Mn substitution of Ga leads to virtual bound states with bandwidth of $\sim $1.5 eV, indicating significant Mn-Ga interactions. We propose that Mn substitution of Ga freezes the Ga motion in the adlayer of the ``1x1'', forcing the extra Ga atoms of the top layer to ``pop up'' and reside at the T$_{4}$ sites, forming the (5x5) reconstruction similar to the DAS structure observed on Si(111) surface. With the Fe/W tip, the regions that contain the incorporated Mn would give rise to the extra bright features that form the $5\sqrt 3 \times 5\sqrt 3 $ structure, due to the higher spin DOS at Mn sites. Implications of these results for understanding the magnetic coupling between Mn atoms in GaN will be discussed at the meeting.