Atomic-scale nature of the (3×3)-ordered GaAs(001):N surface prepared by plasma-assisted molecular-beam epitaxy

In situ scanning tunneling microscopy and time-resolved reflection high-energy electron diffraction measurements were performed to study the nitridation process of the As-terminated GaAs(001)-(2×4) surface by using electron cyclotron resonance plasma-assisted molecular-beam epitaxy. We report the real-space atomic structure of the coherently strained (3×3)-ordered GaN monolayer on GaAs(001) after a limited-exposure nitridation process and the atomically smooth morphology of this nitrided surface. The unique (3×3) phase is found consisting of nitrogen dimers and a regular array of missing nitrogen rows in both [110] and [110] directions.