Initial Stages of Cubic GaN Growth on the GaAs(001) Surface Studied by Scanning Tunneling Microscopy

Nitridation of the GaAs(001) surfaces using an N-atom radio-frequency plasma source is investigated by in situ scanning tunneling microscopy (STM). Atomically flat (3×3) nitrided surfaces commensurate and coherent with the substrate have been achieved on the As-rich (2×4) and (2×6) surfaces. Nitridation proceeds via competing mechanisms of (3×3) ordering and step-etching caused by the N-atoms. The former simply involves N-As exchange, which does not require significant morphology modification, whereas the latter causes the roughening of the substrate under the standard GaN growth conditions. On the Ga-rich surface, the GaN islands immediately form at the step-edges, suggesting the possibility of self-assembled nanostructures of GaN.