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Surface reconstructions of cubic gallium nitride (001) grown by radio frequency nitrogen plasma molecular beam epitaxy under gallium-rich conditions

Cubic GaN has been grown under gallium (Ga)-rich growth conditions using radio frequency nitrogen plasma molecular beam epitaxy on MgO(001) substrates. Reflection high energy electron diffraction patterns indicate the smoothness of the c-GaN surface and show 2× and even 8× periodicities after the growth at sample temperature Ts<200°C and 1×1 at higher temperatures. Scanning tunneling microscopy images reveal a sequence of variant surface reconstructions including c(4×12), 4×7, c(4×16), 4×9, c(4×20), and 4×11. These variant reconstructions correspond to slightly different Ga adatom coverages all less than 1∕4 ML, with 4×11 having the highest, and c(4×12) the lowest Ga coverage. The electronic properties of these six variant reconstructions are investigated, and they are found to have a metallic nature.