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 2x and even 8x periodicities after the growth at sample temperature T-s < 200 degrees C and 1x1 at higher temperatures. Scanning tunneling microscopy images reveal a sequence of variant surface reconstructions including c(4x12), 4x7, c(4x16), 4x9, c(4x20), and 4x11. These variant reconstructions correspond to slightly different Ga adatom coverages all less than 1/4 ML, with 4x11 having the highest, and c(4x12) the lowest Ga coverage. The electronic properties of these six variant reconstructions are investigated, and they are found to have a metallic nature.