Silicon on GaN(0001) and (000(1)over-bar) surfaces

Surface reconstructions and adatom kinetics of silicon on GaN(0001) and (00 01) surfaces are studied by scanning tunneling microscopy, electron diffrac tion, and first-principles calculations. For silicon coverage near 0.5 mono layer, a 2 X 2 structure is observed, and is interpreted in terms of a mode l consisting of a Ga adatom on a monolayer of 3 Ga+ 1Si and a Si-Ga atom in the third layer. For higher silicon coverage, disordered 2 X 2 domains and "1 X 1" domains are found to coexist. After annealing above 300 degreesC t he "1 X 1" regions become dominant and a 4 X 4 structure is seen near step edges. It is concluded that the silicon adatoms tend to reside in subsurfac e sites on the Ga-polar surface. Surface morphology in the presence of Si i s smooth for the (0001) surface but rough for the (0001) surface. This diff erence is attributed to the presence of multiple Ga surface layers in the f ormer case, which enhance surface diffusivities. (C) 2001 American Vacuum S ociety.